                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

NATIVE ECOSYSTEMS COUNCIL; THE         
ECOLOGY CENTER, INC.,
              Plaintiffs-Appellants,
                v.
UNITED STATES FOREST SERVICE, an             No. 04-35375
agency of the U.S. Department of
Agriculture; THOMAS CLIFFORD,                 D.C. No.
                                           CV-02-00080-DWM
supervisor, Helena National
Forest; KATHLEEN MCALLISTER,                   OPINION
Deputy Regional Forester for
Region One U.S. Forest Service;
DALE BOSWORTH, Chief of the
United States Forest Service,
             Defendants-Appellees.
                                       
        Appeal from the United States District Court
                for the District of Montana
        Donald W. Molloy, District Judge, Presiding

                 Argued February 14, 2005
                 Submitted August 11, 2005
                    Seattle, Washington

                   Filed August 11, 2005

 Before: Betty Binns Fletcher, M. Margaret McKeown, and
             Ronald M. Gould, Circuit Judges.

                  Opinion by Judge Gould




                            10409
10412       NATIVE ECOSYSTEMS COUNCIL v. USFS


                        COUNSEL

Thomas J. Woodbury, Forest Defense, P.C., Missoula, Mon-
tana, for the plaintiffs-appellants.

Todd S. Aagaard, Michael T. Gray, Department of Justice,
Washington, D.C., for the defendants-appellees.


                        OPINION

GOULD, Circuit Judge:

   Native Ecosystems Council and The Ecology Center (col-
lectively referred to as “NEC”) appeal the district court’s
grant of summary judgment to the United States Forest Ser-
vice (“Forest Service”) on NEC’s claims in connection with
                NATIVE ECOSYSTEMS COUNCIL v. USFS                    10413
the Forest Service’s approval of the North Elkhorns Vegeta-
tion Treatment Project (“Elkhorn project” or “proposed proj-
ect”). The Elkhorn project is a “wildlife improvement project
involving a timber sale” within the Helena National Forest
and the Elkhorn Wildlife Management Unit (“Elkhorn Wild-
life Unit”), the only Wildlife Management Unit in the
National Forest System. NEC contends that the Forest Ser-
vice’s approval of the Elkhorn project was arbitrary and capri-
cious, in violation of the National Forest Management Act
(“NFMA”), 16 U.S.C. §§ 1600 et seq., the National Environ-
mental Policy Act (“NEPA”), 42 U.S.C. §§ 4321 et seq., and
the Administrative Procedure Act (“APA”), 5 U.S.C. §§ 701-
706, because the project violates the “big game” standards of
the Helena National Forest Plan (“HNF Plan”). NEC also
argues that the Forest Service’s approval of the Elkhorn proj-
ect is arbitrary and capricious because the project will
threaten the forest-wide viability of the Northern Goshawk.
We have jurisdiction pursuant to 28 U.S.C. § 1291. We
reverse and remand.

                                     I

   The Helena National Forest comprises 975,088 acres of
west-central Montana and includes a broad expanse of the
Elkhorn Mountains. The Helena National Forest is managed
in accord with the HNF Plan, adopted pursuant to NFMA in
1986.1 Among other requirements, the HNF Plan contains
  1
   NFMA sets the statutory framework for the management of our
National Forest lands. 16 U.S.C. § 1604. NFMA establishes a two-step
process for forest planning. First, NFMA requires the Forest Service to
develop and maintain a Forest Plan for each unit of the National Forest
System. See id. § 1604(a). Each Forest Plan must set forth multiple use
objectives to ensure recreation uses, maintain a diversity of plant and ani-
mal species, maintain the viability of native species, and enable timber
yield from the forests. See id. § 1604(e). NFMA also requires that the For-
est Service adopt regulations specifying guidelines for forest plans. Id.
§ 1604(g)(3); see 36 C.F.R. § 219 et seq.
  Second, under NFMA, the Forest Service implements each Forest Plan
by approving or disapproving site-specific actions. All proposed projects
must be consistent with the overall forest plan. 16 U.S.C. § 1604(i).
10414           NATIVE ECOSYSTEMS COUNCIL v. USFS
standards relating to the security of big game species such as
elk, including the requirement that each elk herd have at least
thirty-five percent “hiding cover.”2 The HNF Plan’s elk hid-
ing cover standard is central to NEC’s claims, and we exam-
ine it in detail in Section II.

   The Elkhorn Mountains are also the home of the only des-
ignated Wildlife Management Unit in our National Forest
System, the Elkhorn Wildlife Unit. In 1976, Congress
directed the Forest Service to evaluate 77,346 acres of Helena
and Deerlodge National Forests for designation as a Wilder-
ness Area. Wilderness Act of 1976, Pub. L. No. 94-557, 90
Stat. 2633, 2637. Prompted by “the presence of valuable wild-
life resources, and the predominance of public concern for
wildlife values in the area,” the Forest Service instead recom-
mended the establishment of a special management unit with
a management direction emphasizing wildlife. The subse-
quently created Elkhorn Wildlife Unit encompasses areas of
both the Helena and Deerlodge National Forests in Montana,
including the area of the proposed project. The Elkhorn Wild-
life Unit has its own standards, with which any site-specific
projects must comply and which have been incorporated into
the HNF Plan. Relevant to this appeal, the Forest Service is
only to consider “land management activities” in the Elkhorn
Wildlife Unit when “they are compatible with management
direction for wildlife.” The Elkhorn Wildlife Unit is also gen-
erally “unsuitable for timber management, because the land is
proposed for use that precludes timber harvest on the pro-
grammed basis.”
  2
   “Hiding cover” is a “timber stand which conceals 90 percent or more
of a standing elk at 200 feet.” The Elkhorn Mountains are one of the most
heavily-hunted areas in the State of Montana, and hiding cover is one of
several elements of elk security in the Elkhorn Mountains. Elk security is
the “protection inherent in any situation that allows elk (and presumably
deer) to remain in defined areas despite an increase in stress or disturbance
associated with the hunting season or other human activities.”
                NATIVE ECOSYSTEMS COUNCIL v. USFS                    10415
   In 1996, the Forest Service proposed an amendment to the
Helena and Deerlodge National Forest Plans called the “Elk-
horn Forest Plan Amendment,” seeking to alter the direction
of the Elkhorn Wildlife Unit from its wildlife emphasis to a
more general “ecosystem management.”3 The district court
upheld a challenge by environmental groups, concluding that
the Plan amendment was “significant” and that the Forest Ser-
vice had violated NEPA by not preparing an Environmental
Impact Statement (“EIS”) for the proposed amendment.4 Am.
Wildlands v. U.S. Forest Serv., No. CV 97-160-M-DWM,
1999 U.S. Dist. LEXIS 22243, at *22-*23 (D. Mont. 1999).
The Forest Service thereafter abandoned the Elkhorn Forest
Plan Amendment. However, the Forest Service was not pre-
cluded by the district court’s decision from pursuing future
projects within the Elkhorn Wildlife Unit, so long as any pro-
posed projects were consistent with the 1986 HNF Plan,
NFMA, and NEPA.

  The Forest Service proposed the Elkhorn project in 2000.
After completing an Environmental Impact Statement (“EIS”)
and Record of Decision (“ROD”) in 2001, the Forest Supervi-
sor chose Alternative 2, the harvesting of 655 acres within a
  3
     This would have placed other goals and objectives such as mining, tim-
ber, and grazing on par with wildlife conservation.
   4
     Unlike NFMA, NEPA does not “mandat[e] that agencies achieve par-
ticular substantive environmental results.” Marsh v. Or. Natural Res.
Council, 490 U.S. 360, 371 (1989). Rather, agencies must comply with
NEPA’s procedural requirements, ensuring both that the agency “carefully
consider” a project’s environment impacts, and that the “relevant informa-
tion will be made available,” so that the public can “play a role in both the
decisionmaking process and the implementation of that decision.” Robert-
son v. Methow Valley Citizens Council, 490 U.S. 332, 349 (1989).
   Among other procedural requirements, NEPA requires that federal
agencies prepare an EIS for major federal actions significantly affecting
the quality of the human environment. 42 U.S.C. § 4332(2)(C). An EIS
must provide a “full and fair discussion of significant environmental
impacts,” and inform “decisionmakers and the public of the reasonable
alternatives which would avoid or minimize adverse impacts or enhance
the quality of the human environment.” 40 C.F.R. § 1502.1.
10416           NATIVE ECOSYSTEMS COUNCIL v. USFS
755-acre area of forest in the northwest corner of the Elkhorn
Wildlife Unit.5 Because the Elkhorn Wildlife Unit is classified
under the HNF Plan as “unsuitable” for timber harvest, the
Elkhorn project is not a “timber sale per se, it is a wildlife
habitat improvement project that will involve a timber sale
(commercial thinning) as the tool to achieve part of the
desired condition.” The Forest Supervisor concluded that such
land can be logged under NFMA for the “purpose of meeting
other objectives if the Forest Plan establishes that such actions
are appropriate.” (citing 36 C.F.R. § 219.27 (1999)). The proj-
ect’s stated purpose is to improve wildlife habitat through the
“rejuvenat[ion]” of “the winter range forage base for species
such as deer, elk, and moose,” and the creation of “a sustain-
able forest structure that would eventually provide [more]
suitable habitat” for other wildlife species. The proposed proj-
ect would create a “broad swath of open forest (approximately
3 miles long and 1/4 to mile wide),” reconstruct a road, and
construct a non-motorized loop trail.

   The 2001 EIS concluded that the project complied with the
HNF Plan’s “Big Game” requirements. Specifically, the EIS
concluded that the project would leave the affected elk herd,
the Sheep Creek elk herd, with fifty-seven percent hiding
cover, above the thirty-five percent hiding cover minimum
required by the HNF Plan.6

  After the Forest Service published the Elkhorn project EIS
and ROD, NEC filed an administrative appeal, which was
denied. NEC then filed suit in the United States District Court
  5
    The section of forest involved is not old-growth forest.
  6
    According to the EIS, the Sheep Creek elk herd has 14,112 acres of
hiding cover available to it, of which the Elkhorn project would eliminate
620 acres. The EIS used the 24,000 acres of the 46,000 Sheep Creek Elk
Herd Unit within the Helena National Forest as the denominator of its hid-
ing cover calculation. Thus, the EIS concluded that the Sheep Creek elk
herd has a hiding cover percentage of fifty-nine percent, and, after the
action approved by the Forest Service, would still have fifty-seven percent
hiding cover.
             NATIVE ECOSYSTEMS COUNCIL v. USFS           10417
for the District of Montana, arguing that the Forest Service’s
approval of the Elkhorn project violated NEPA, NFMA, and
the APA.

   The parties filed cross-motions for summary judgment. The
district court granted the Forest Service’s motion, concluding
that the agency’s analysis of the proposed project’s impacts
was sufficient to meet the requirements of NFMA and NEPA
as well as the requirements of the HNF Plan. The district
court noted that the Forest Service had altered the acreage
denominator of its elk hiding cover analysis from previous
hiding cover analyses, which had concluded that the Sheep
Creek elk herd was generally below the hiding cover mini-
mum as calculated over the herd’s entire range. The Forest
Service’s change to the 2001 calculation methodology conse-
quently boosted the percentage of cover present after the proj-
ect to within the range allowable under the HNF Plan. The
district court called the Forest Service’s change “convenient,
or even suspicious,” but concluded that “its appropriateness is
not something this court can determine.” This timely appeal
followed.

                              II

   NEC argues that the Elkhorn project does not comply with
the HNF Plan’s “big game” hiding cover requirements and
therefore does not comply with NFMA. See 16 U.S.C.
§ 1604(i). NEC also argues that the Elkhorn project EIS is
deficient under NEPA because it used an incorrect hiding
cover calculation to reach the conclusion that the project com-
plied with the HNF Plan.

                              A

  We review de novo a grant of summary judgment. Ground
Zero Ctr. for Non-Violent Action v. U.S. Dep’t of Navy, 383
F.3d 1082, 1086 (9th Cir. 2004). Our review of agency
decision-making under NFMA is governed by the judicial
10418         NATIVE ECOSYSTEMS COUNCIL v. USFS
review provisions of the APA because NFMA does not con-
tain an express provision for judicial review. 5 U.S.C.
§ 706(2)(A); Gifford Pinchot Task Force v. U.S. Fish and
Wildlife Service, 378 F.3d 1059, 1065 (9th Cir. 2004). Under
the APA, we may set aside agency action only if it was “arbi-
trary, capricious, an abuse of discretion, or otherwise not in
accordance with law.” Wilderness Soc’y v. U.S. Fish & Wild-
life Serv., 353 F.3d 1051, 1059 (9th Cir. 2003) (en banc).
Although the arbitrary and capricious standard is a “narrow
one,” we are required to “engage in a substantial inquiry[,] . . .
a thorough, probing, in-depth review.” Citizens to Preserve
Overton Park, Inc. v. Volpe, 401 U.S. 402, 415-16 (1971),
overruled on other grounds by Califano v. Sanders, 430 U.S.
99, 105 (1977). To have not acted in an arbitrary and capri-
cious manner, the agency must present a “rational connection
between the facts found and the conclusions made.” Nat’l
Wildlife Fed’n v. U.S. Army Corps of Eng’rs, 384 F.3d 1163,
1170 (9th Cir. 2004).

   Agencies are entitled to deference to their interpretation of
their own regulations, including Forest Plans. Forest Guard-
ians v. U.S. Forest Serv., 329 F.3d 1089, 1097, 1099 (9th Cir.
2003); Idaho Sporting Cong. v. Thomas, 137 F.3d 1146, 1154
(9th Cir. 1998). However, an agency’s interpretation “does
not control, where . . . it is plainly inconsistent with the regu-
lation at issue.” Friends of Southeast’s Future v. Morrison,
153 F.3d 1059, 1069 (9th Cir. 1998); see Thomas Jefferson
Univ. v. Shalala, 512 U.S. 504, 512 (1994) (explaining that no
deference is due to an agency interpretation that contradicts
the regulation’s plain language). We “may not defer to an
agency decision that ‘is without a substantial basis in fact’ ”
and cannot uphold a decision based on a “clear error of judg-
ment.” Sierra Club v. U.S. EPA, 346 F.3d 955, 961 (9th Cir.
2003) (quoting Fed. Power Comm’n v. Fla. Power & Light
Co., 404 U.S. 453, 463 (1972) and Motor Vehicle Mfrs. Ass’n
of the U.S. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43
(1983)).
             NATIVE ECOSYSTEMS COUNCIL v. USFS           10419
   Our review for compliance with NEPA also occurs under
the APA, which authorizes courts to set aside agency actions
adopted “without observance of procedure required by law.”
Ctr. for Biological Diversity v. U.S. Forest Serv., 349 F.3d
1157, 1165 (9th Cir. 2003) (quoting 5 U.S.C. § 706(2)(D)). In
reviewing the adequacy of an EIS, we apply the “rule of rea-
son” standard, which requires “a pragmatic judgment whether
the EIS’s form, content and preparation foster both informed
decision-making and informed public participation.” Califor-
nia v. Block, 690 F.2d 753, 761 (9th Cir. 1982). Stated differ-
ently, our “task is to ensure that the agency has taken a ‘hard
look’ at the potential environmental consequences of the pro-
posed action.” Klamath-Siskiyou Wildlands Ctr. v. Bureau of
Land Mgmt., 387 F.3d 989, 993 (9th Cir. 2004) (citation omit-
ted).

                              B

   The Elkhorn Mountains are one of the most heavily hunted
areas in the State of Montana. The HNF Plan includes several
standards to maintain or improve big game security and to
maintain adequate big game habitat for species like elk and
mule deer:

    Big Game

    1. On important summer . . . and winter range, ade-
    quate thermal and hiding cover will be maintained to
    support the habitat potential.

    2. An environmental analysis for project work will
    include a cover analysis. The cover analysis should
    be done on a drainage or elk herd unit basis. . . .

    3. Subject to hydrologic and other resource con-
    straints, elk summer range will be maintained at 35
    percent or greater hiding cover and areas of winter
10420          NATIVE ECOSYSTEMS COUNCIL v. USFS
      range will be maintained at 25 percent or greater
      thermal cover in drainages or elk herd units.

      4. Implement an aggressive road management
      program to maintain or improve big game security.
      . . .[7]

                                   1

   [1] The 2001 EIS describes the hiding cover standard as
“not [a] very meaningful” measure of the Forest Service’s
duty to provide for elk security in the Helena National Forest
and Elkhorn Wildlife Unit. It is well-settled that the Forest
Service’s failure to comply with the provisions of a Forest
Plan is a violation of NFMA. As NFMA makes plain,
“[r]esource plans, permits, contracts, and other instruments
for the use and occupancy of National Forest System lands
shall be consistent with the land management plans.” 16
U.S.C. § 1604(i); see also Neighbors of Cuddy Mountain v.
Alexander, 303 F.3d 1059, 1062 (9th Cir. 2002) (“Specific
projects, such as the Grade/Dukes timber sale, must be ana-
lyzed by the Forest Service and the analysis must show that
each project is consistent with the plan.”); Neighbors of
Cuddy Mountain v. U.S. Forest Serv., 137 F.3d 1372, 1377-78
(9th Cir. 1998) (holding that the Forest Service was not in
compliance with NFMA where its site-specific project was
inconsistent with the forest plan of the entire forest); Friends
of Southeast’s Future, 153 F.3d at 1068 n.4 (“16 U.S.C.
§ 1604(i) plainly imposes a legal obligation on the Forest Ser-
vice to ensure that timber sales are consistent with the rele-
vant Forest Plan.”).

  Our scope of review does not include attempting to discern
  7
    We refer to each of these standards as Big Game Standard #1, #2, #3,
or #4. We recite only the beginning of Big Game Standard #4, which con-
tinues and provides a maximum open road density for big game hunting
season that depends on the percentage of hiding cover in an area.
                NATIVE ECOSYSTEMS COUNCIL v. USFS                   10421
which, if any, of a validly-enacted Forest Plan’s requirements
the agency thinks are relevant or meaningful. If the Forest
Service thinks any provision of the 1986 HNF Plan is no lon-
ger relevant, the agency should propose amendments to the
HNF Plan altering its standards, in a process complying with
NEPA and NFMA, rather than discount its importance in
environmental compliance documents.

                                    2

   [2] The administrative record shows that there are 14,112
acres of potential hiding cover in the 45,675 acre Sheep Creek
elk herd unit or drainage, and that the proposed project would
subtract 620 acres, leaving 13,492 acres of hiding cover. NEC
does not dispute these figures. Rather, NEC takes issue with
the Forest Service’s calculation denominator: the area over
which the agency determined the hiding cover percentage.
The question is whether we can reasonably discern from the
record that the Forest Service complied with the HNF Plan’s
Big Game minimum hiding cover standard, HNF Plan Big
Game Standard #3, and thereby complied with NFMA. Motor
Vehicle Mfrs. Ass’n, 463 U.S. at 43 (holding that courts must
“ ‘uphold a decision of less than ideal clarity if the agency’s
path may reasonably be discerned’ ” (quoting Bowman
Transp., Inc. v. Arkansas-Best Freight Sys., 419 U.S. 281, 286
(1974)).

   We are unable to determine from the record that the agency
is complying with the forest plan standard. The HNF Plan’s
hiding cover standard can be read to require the hiding cover
percentage be calculated over the entire elk herd unit or drain-
age, or only over the summer range portion of that elk herd
unit.8 However, the Elkhorn Project EIS and ROD did not cal-
  8
   NEC argues that the hiding cover analysis should have been completed
over the entire Sheep Creek herd unit, or 45,675 acres, because the stan-
dard must “be maintained at 35 percent or greater . . . in drainages or elk
herd units.” If the 45,675 acre Sheep Creek herd unit or drainage was used
10422          NATIVE ECOSYSTEMS COUNCIL v. USFS
culate hiding cover over either: The EIS does not include a
hiding cover calculation for the Sheep Creek elk herd’s entire
range or drainage, nor does the EIS include a mathematical
determination of the Sheep Creek herd’s summer range from
which to calculate the hiding cover percentage. Instead, the
EIS relied on the fact that about 24,000 acres of the 46,000-
acre Sheep Creek Elk Herd Unit are within the Helena
National Forest and estimated that the Sheep Creek elk herd’s
summer range was, as the Forest Service said in its briefing,
“roughly equivalent” to the HNF Forest boundary. This
24,000 acre denominator was the baseline from which the
agency reached its conclusion that the project complied with
the Forest Plan standard. In addition, the 2001 EIS measured
hiding cover within the Helena National Forest area that cor-
responds to the 24,000 acre denominator, but not whether any
hiding cover existed in the area inhabited by the Sheep Creek
herd beyond the boundary of the Helena National Forest.

   An agency’s position that is contrary to the clear language
of a Forest Plan is not entitled to deference. Friends of South-
east’s Future, 153 F.3d at 1069. Here, the Forest Service’s
hiding cover calculations considered only the section of the
Sheep Creek elk herd’s range within the boundaries of the
Helena National Forest and not the parts of the elk herd’s
range located on private or other, non-HNF public lands. The
agency’s interpretation is inconsistent with the language of
the forest plan:

as the calculation denominator, the hiding cover percentage would be
thirty percent, under the HNF Plan minimum percentage of thirty-five per-
cent, before the effects from the proposed project. The Forest Service
argues that only the “summer range” portion of the elk herd unit need be
included in the hiding cover calculation for it to comply with the hiding
cover standard, because the thirty-five percent minimum is only required
over the herd’s summer range (“elk summer range will be maintained at
35 percent or greater hiding cover”). The Forest Service’s interpretation
of the Forest Plan language in this regard is not plainly erroneous or
facially inconsistent with the Plan’s language. See Forest Guardians, 329
F.3d at 1099.
             NATIVE ECOSYSTEMS COUNCIL v. USFS           10423
    An environmental analysis for project work will
    include a cover analysis. The cover analysis should
    be done on a drainage or elk herd unit basis. . . .
    Subject to hydrologic and other resource constraints,
    elk summer range will be maintained at 35 percent
    or greater hiding cover . . . in drainages or elk herd
    units.

(emphasis added). The hiding cover standard does not allow
the Forest Service to exclude private and other non-HNF pub-
lic lands within the Sheep Creek elk herd’s range from its hid-
ing cover calculation perimeters, as the agency did in the
Elkhorn project EIS.

   [3] In Neighbors of Cuddy Mountain v. U.S. Forest Service,
the Forest Plan of the Payette National Forest required the
Forest Service to show that any approved projects would
leave five-percent old growth forest within each affected “pi-
leated woodpecker’s home range.” 137 F.3d at 1377-78. The
Forest Service concluded that the approved project would
meet the Forest Plan standard by calculating the minimum
old-growth percentage using the area of the proposed timber
sale rather than the woodpecker’s range. Id. We reversed the
district court’s grant of summary judgment to the Forest Ser-
vice, holding that, inter alia, the agency “did not demonstrate
that the Grade/Dukes project would be consistent with the
Payette LRMP, and thus it failed to comply with the NFMA.”
Id. at 1378. As in Neighbors of Cuddy Mountain v. U.S. For-
est Service, in the 2001 EIS in this case, the Forest Service
used an incorrect denominator in attempting to comply with
the Forest Plan standard, calculating the Sheep Creek elk
herd’s hiding cover over only the sections of the Sheep Creek
elk herd within the Helena National Forest boundaries, rather
than calculating the percentage over the Sheep Creek elk
herd’s “drainage or elk herd unit.” The EIS thus did not
ensure that the Elkhorn project would comply with the HNF
Plan and failed to comply with NFMA.
10424           NATIVE ECOSYSTEMS COUNCIL v. USFS
   Under NFMA, the Forest Service calculations need not be
perfect. Forest Guardians, 329 F.3d at 1099. However, we
must still be able reasonably to ascertain from the record that
the Forest Service is in compliance with the HNF Plan stan-
dard. SEC v. Chenery Corp., 332 U.S. 194, 196-197 (1947)
(“If the administrative action is to be tested by the basis upon
which it purports to rest, that basis must be set forth with such
clarity as to be understandable. It will not do for a court to be
compelled to guess at the theory underlying the agency’s
action; nor can a court be expected to chisel that which must
be precise from what the agency has left vague and indeci-
sive.”). In this case, we cannot tell from the administrative
record whether or not the Forest Service complied with the
hiding cover standard. The Forest Service has given several
substantially varying perimeters of how it measures whether
the Sheep Creek elk herd’s hiding cover standard is met. In
contrast to its EIS calculation, the Forest Service asserts in its
briefing that the Sheep Creek elk herd’s summer range is
actually 29,591 acres, but that the effect of the proposed proj-
ect will still leave the herd with forty-three percent hiding
cover on its summer range. In contrast to that figure, the
record also includes two previous Forest Service calculations
of the Sheep Creek summer range, in 1995 and 1996, respec-
tively, as being 34,220 acres. Previous hiding cover analyses
done over the Sheep Creek elk herd and using the entire elk
herd unit as its denominator had concluded that the elk herd’s
hiding cover was below the thirty-five percent minimum set
by the HNF Plan.9 As recently as 1995-96, the Forest Service
concluded that the Helena National Forest was generally lack-
ing in sufficient hiding cover, and noted that “it is very diffi-
cult for most elk herd units on the Deerlodge and Helena
  9
    Both a 1995 Environmental Assessment (“EA”) and 1996 EA listed the
Sheep Creek herd unit as having twenty-two percent hiding cover. Both
of these earlier analyses determined hiding cover generally, for an average
of all seasons, without calculating the summer and winter range cover,
because the analyses were done to determine compliance with HNF Plan
Big Game Standard #4, which sets the standard for hiding cover as a ratio
to open road density and does not require a summer/winter calculation.
               NATIVE ECOSYSTEMS COUNCIL v. USFS                  10425
Forests to meet Forest Plan standards due to inherently low
cover and a high degree of access.” The Forest Service has
not presented any rational explanation for its calculation
change and its varying calculations do not assist us in our
attempt to discern whether the agency has complied with the
HNF Plan.

   [4] Our review of the record did not disclose any other
basis for the Forest Service’s claim that it ensured that the
project complied with the standard. The two maps of the area
do not serve as documentation of how the Forest Service
reached its 24,000 acre calculation in the EIS, which in any
event the Service has now disavowed, or the Forest Service’s
more recent 29,591 acre calculation. Neither map has a leg-
end, an accompanying study, or any other explanation for
how the summer range figure was calculated by the Forest Ser-
vice.10 Given the Forest Service’s contradictory calculations
and the otherwise opaque nature of the record on the factual
basis for the Forest Service’s analysis of its compliance with
the hiding cover standard, we cannot reasonably determine
that the Forest Service has complied with the HNF Plan. Nat’l
Wildlife Federation, 384 F.3d at 1170 (holding that agencies
must articulate a “rational connection between the facts found
and the conclusions made”).

                                   C

   We next address whether the Elkhorn project EIS complied
with NEPA. As we explained in the above NFMA analysis,
the EIS used a calculation denominator that is inconsistent
with the hiding cover requirement of the HNF Plan. The HNF
  10
    The absence of any support for the Forest Service’s summer range cal-
culation is highlighted by the Sheep Creek herd’s winter range determina-
tion, which was based on a ten-year USFS study tracking the Sheep Creek
herd using radio-collars and which is not challenged by NEC on appeal.
The Forest Service admits that, although the same study generally
described the Sheep Creek elk herd’s summer range, it did not calculate
it.
10426        NATIVE ECOSYSTEMS COUNCIL v. USFS
plan hiding cover standard does not allow the Forest Service
to calculate elk hiding cover over only the part of the elk
herd’s range within the Helena National Forest, excluding pri-
vate and other non-HNF public lands within the Sheep Creek
elk herd’s summer range from its calculations, as the agency
did in the EIS.

   [5] To take the required “hard look” at a proposed project’s
effects, an agency may not rely on incorrect assumptions or
data in an EIS. 40 C.F.R. § 1500.1(b) (“Accurate scientific
analysis, expert agency comments, and public scrutiny are
essential to implementing NEPA.”). By the Forest Service’s
estimate, the 24,000 acre calculation used in the EIS is more
than 5,000 acres smaller than the area the Forest Service now
argues is the Sheep Creek elk herd’s summer range. The
agency is required to “insure the professional integrity,
including scientific integrity, of the discussions and analyses
in environmental impact statements.” 40 C.F.R. § 1502.24.
The Forest Service did not disclose in the Elkhorn project EIS
that its hiding cover measurement was done over an improper
(and as it now acknowledges, smaller) area. Lands Council v.
Powell, 395 F.3d 1019, 1032 (9th Cir. 2005) (holding that
NEPA requires “up-front disclosures of relevant shortcomings
in the data or models” and that withholding such information
violates the statute). The Forest Service’s use of a hiding
cover denominator in the EIS other than that allowed by the
HNF Plan arbitrarily and capriciously skewed the EIS’s elk
herd hiding cover percentage. Consequently, the Elkhorn
project EIS did not provide a “full and fair” discussion of the
potential effects of the project on elk hiding cover and did not
“inform[ ] decisionmakers and the public of the reasonable
alternatives which would avoid or minimize adverse impacts”
on the Sheep Creek elk herd. Klamath-Siskiyou Wildlands
Ctr., 387 F.3d at 993 (quoting 40 C.F.R. § 1502.1); see also
Animal Def. Council v. Hodel, 840 F.2d 1432, 1439 (9th Cir.
1988) (“Where the information in the initial EIS was so
incomplete or misleading that the decisionmaker and the pub-
lic could not make an informed comparison of the alterna-
               NATIVE ECOSYSTEMS COUNCIL v. USFS                   10427
tives, revision of an EIS may be necessary to provide a
reasonable, good faith, and objective presentation of the sub-
jects required by NEPA.”) (internal quotation marks omitted),
amended by 867 F.2d 1244 (9th Cir. 1989).

                                   III

   [6] The decision by the Forest Service to approve the Elk-
horn project violates both NFMA and NEPA. In an adminis-
trative appeal, we cannot divine the grounds for government
decisions that are not explained or apparent. The Forest Ser-
vice has failed to provide us with a satisfactory explanation
supported by the record showing the necessary rational basis
for its hiding cover calculation. Motor Vehicle Mfrs. Ass’n,
463 U.S. at 43 (holding that agency actions must be reversed
as arbitrary and capricious when the agency fails to “examine
the relevant data and articulate a satisfactory explanation for
its action including a rational connection between the facts
found and the choice made”) (internal quotation marks omit-
ted). The Elkhorn project EIS utilized a calculation denomina-
tor that was plainly inconsistent with the Forest Plan standard.
Neighbors of Cuddy Mountain v. U.S. Forest Serv., 137 F.3d
at 1377-78. In our own review of the administrative record,
we are unable to discern that the Forest Service’s hiding cover
calculations complied with the requirements of the HNF Plan.
Fed. Power Comm’n v. Transcontinental Gas Pipe Line
Corp., 423 U.S. 326, 331 (1976) (per curiam) (“If the decision
of the agency is not sustainable on the administrative record
made, then the . . . decision must be vacated and the matter
remanded . . . for further consideration.”) (alteration in the
original) (internal quotation marks omitted). Because the
record does not include a basis for the Forest Service’s con-
clusion that the project will not violate the HNF Plan’s hiding
cover standard, the agency’s approval of the project was arbi-
trary and capricious and a violation of NFMA.11
  11
    Because the Forest Service has not ensured the project is in compli-
ance with the elk hiding cover standard, it has also acted in an arbitrary
10428           NATIVE ECOSYSTEMS COUNCIL v. USFS
   [7] The Elkhorn project EIS is inadequate under NEPA
because, by using a hiding cover calculation denominator that
is inconsistent with that required by the HNF plan, the agency
did not take a “hard look” at the project’s true effect and
failed to inform the public of the project’s environmental
impact.

   We reverse and remand this case to the Forest Service for
further proceedings consistent with this opinion.12

   REVERSED and REMANDED.




and capricious manner in violation of the Elkhorn Wildlife Unit direction
that projects only be considered when they are compatible with the man-
agement direction for wildlife. The proposed project fails to abide by the
HNF Plan’s elk hiding cover standard, in the area specifically delineated
by the Forest Service to protect that species.
   12
      It is unnecessary for us to reach NEC’s argument that the Forest Ser-
vice’s approval of the proposed project was arbitrary and capricious on the
theory that the agency has failed to protect the forest-wide viability of the
Northern Goshawk. NEC relied on evidence outside the administrative
record in support of its argument of inadequate monitoring of the Northern
Goshawk in the Helena National Forest. Upon remand, subject to agency
regulations, NEC may have the opportunity to introduce evidence on gos-
hawk monitoring before the agency in the first instance. We deny NEC’s
motion to supplement the record on appeal.
