                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

BURLINGTON NORTHERN & SANTA            
FE RAILWAY COMPANY,
                 Plaintiff-Appellee,
                v.                           No. 05-16755
CHARLES VAUGHN, Chairman of the
Hualapai Indian Tribe, a federally            D.C. No.
                                           CV-04-02227-EHC
recognized Indian Tribe; WANDA
                                              OPINION
EASTER, Finance Director of the
Hualapai Indian Tribe, a federally
recognized Indian Tribe,
            Defendants-Appellants.
                                       
        Appeal from the United States District Court
                 for the District of Arizona
         Earl H. Carroll, District Judge, Presiding

                 Argued and Submitted
       October 16, 2007—San Francisco, California

                  Filed December 7, 2007

    Before: Arthur L. Alarcón, David R. Thompson, and
            Richard C. Tallman, Circuit Judges.

                 Opinion by Judge Tallman




                            16105
16108        BURLINGTON NORTHERN v. VAUGHN


                      COUNSEL

Susan M. Williams (argued), Sarah S. Works, Williams &
Works, P.A., Corrales, New Mexico, for the appellants.
                BURLINGTON NORTHERN v. VAUGHN              16109
Charles G. Cole (argued), Alice E. Loughran, Amber B.
Blaha, Steptoe & Johnson LLP, Washington, D.C.; Paul J.
Mooney, Jim L. Wright, Fennemore Craig, P.C., Phoenix,
Arizona, for the appellee.


                           OPINION

TALLMAN, Circuit Judge:

   The Burlington Northern & Santa Fe Railway Company
(BNSF) brought suit against two officials of the Hualapai
Indian Tribe, Charles Vaughn and Wanda Easter (the tribal
officials), seeking declaratory and injunctive relief against
their efforts to enforce or collect the Hualapai Tribe’s posses-
sory interest tax against BNSF for use of the railroad’s right-
of-way through the reservation. The tribal officials filed a
motion to dismiss, which the district court denied. The tribal
officials bring this appeal.

   We address the novel jurisdictional question whether, under
Cohen v. Beneficial Industrial Loan Corp., 337 U.S. 541
(1949), denial of a tribal sovereign immunity claim is appeal-
able on an interlocutory basis as a collateral order. We hold
that it is and proceed to review the district court’s ruling on
the merits. We affirm the district court’s ruling that tribal sov-
ereign immunity does not bar suit against Easter, who is alleg-
edly responsible for enforcing the tax at issue in this suit, but
reverse with regard to Vaughn, the Tribe’s Chairman, who
has no alleged enforcement responsibilities to actually collect
the tax. The tribal officials also appeal the district court’s
denial of their exhaustion of tribal remedies claim. However,
they do not assert an adequate basis to permit us to exercise
jurisdiction over that claim now, and we dismiss the remain-
der of this interlocutory appeal.
16110            BURLINGTON NORTHERN v. VAUGHN
                                  I

   Viewed in the light most favorable to BNSF, as required on
a motion to dismiss, see Hydrick v. Hunter, 500 F.3d 978, 985
(9th Cir. 2007), the record reveals the following facts. BNSF1
operates its railroad on a congressionally granted right-of-way
through Arizona that crosses the Hualapai Indian Reservation.
BNSF owns title to the right-of-way, free of all claims by the
Tribe.

   In 1989, the Hualapai Tribal Council enacted a tax by ordi-
nance which imposes a 7% tax on the value of certain “pos-
sessory interests” within the Reservation. At oral argument,
counsel for the Tribe asserted the tax was intended to be in the
nature of a use tax to reimburse the Tribe for the cost of
attending railway accidents or blockages since the mainline
hosts upward of eighty trains daily that pass at one point
through the heart of the tribal administrative center. In 1991,
BNSF brought suit challenging the Tribe’s authority to apply
the tax to the railroad’s right-of-way. The parties settled and
BNSF agreed to pay a lump sum to the Tribe in lieu of any
taxes, interest, and penalties that might otherwise have been
assessed against it during tax years 1990 through 2001.

   On July 24, 2002, after the settlement agreement had
expired, Wanda Easter, the Tribe’s finance director, sent tax
registration forms to BNSF. BNSF notified the Tribe that it
disputed the Tribe’s jurisdiction to tax BNSF’s operation of
the right-of-way. The parties attempted to resolve their dis-
agreement, but were unsuccessful.

   BNSF subsequently filed a complaint in the United States
District Court for the District of Arizona seeking declaratory
and injunctive relief against the Tribe’s efforts to enforce or
collect the tax. The tribal officials responded with a motion to
dismiss, claiming that: 1) the suit is barred by tribal sovereign
  1
   References to BNSF include BNSF and its predecessors in interest.
                BURLINGTON NORTHERN v. VAUGHN               16111
immunity, 2) BNSF failed to exhaust tribal remedies, and 3)
the tax does not violate federal law. The district court denied
the motion, holding that: 1) tribal sovereign immunity did not
bar BNSF’s claims against the tribal officials, 2) BNSF was
not required to exhaust tribal remedies because the tribal court
“plainly” lacked jurisdiction, and 3) BNSF’s allegation that
the tax is unenforceable against it was sufficient to state a
claim for relief. The tribal officials appealed.

                                II

                                A

   [1] Our jurisdiction is circumscribed by 28 U.S.C. § 1291,
which provides: “The courts of appeals . . . shall have juris-
diction of appeals from all final decisions of the district courts
of the United States . . . .” A district court’s denial of a motion
to dismiss is not a final decision within the meaning of 28
U.S.C. § 1291. Credit Suisse v. U.S. Dist. Court for the Cent.
Dist. of Cal., 130 F.3d 1342, 1345-46 (9th Cir. 1997). None-
theless, the Supreme Court has recognized an exception to the
final judgment rule for that “small class [of orders] which
finally determine claims of right separable from, and collat-
eral to, rights asserted in the action.” Cohen, 337 U.S. at 546.

   [2] We have not previously decided whether a district
court’s order denying a motion to dismiss on tribal sovereign
immunity grounds is a collateral order which may be
reviewed on an interlocutory basis. The Tribe persuasively
argues that by analogy to qualified immunity appeals under
civil rights claims, the rule should be the same when an
adverse decision is rendered denying tribal sovereign immu-
nity as a complete defense to proceeding with the litigation.
See Mitchell v. Forsyth, 472 U.S. 511 (1985). We agree.

   [3] As commonly expressed, the collateral order doctrine
established in Cohen permits interlocutory review of an order
that “conclusively determine[s] the disputed question,
16112           BURLINGTON NORTHERN v. VAUGHN
resolve[s] an important issue completely separate from the
merits of the action, and [is] effectively unreviewable on
appeal from a final judgment.” Coopers & Lybrand v. Live-
say, 437 U.S. 463, 468 (1978). All three factors are met in this
case.

   [4] The district court’s order “conclusively determine[d]
the disputed question,” that is, whether the tribal officials are
immune from suit, because “there will be nothing in the sub-
sequent course of the proceedings in the district court that can
alter the court’s conclusion that the defendant[s are] not
immune.” See Mitchell, 472 U.S. at 527.

   [5] The district court’s order is also “effectively unreview-
able on appeal from a final judgment.” See Coopers & Lyb-
rand, 437 U.S. at 468. Tribal sovereign immunity is rooted in
federal common law and “is a necessary corollary to Indian
sovereignty and self-governance.” Three Affiliated Tribes of
the Ft. Berthold Reservation v. Wold Eng’g, 476 U.S. 877,
890 (1986). Indian tribes, and tribal officials acting within the
scope of their authority, are immune from lawsuits or court
process in the absence of congressional abrogation or tribal
waiver. Kiowa Tribe of Okla. v. Mfg. Techs., Inc., 523 U.S.
751, 754 (1998); United States v. Yakima Tribal Court, 806
F.2d 853, 861 (9th Cir. 1986). As with absolute, qualified, and
Eleventh Amendment immunity, tribal sovereign immunity
“is an immunity from suit rather than a mere defense to liabil-
ity; and . . . it is effectively lost if a case is erroneously per-
mitted to go to trial.” See P.R. Aqueduct & Sewer Auth. v.
Metcalf & Eddy, Inc., 506 U.S. 139, 143-44 (1993) (quoting
Mitchell, 472 U.S. at 526); Osage Tribal Council v. U.S.
Dep’t of Labor, 187 F.3d 1174, 1179-80 (10th Cir. 1999);
Tamiami Partners, Ltd. v. Miccosukee Tribe of Indians of
Fla., 63 F.3d 1030, 1050 (11th Cir. 1995) (“Tribal sovereign
immunity would be rendered meaningless if a suit against a
tribe asserting its immunity were allowed to proceed to
trial.”).
                BURLINGTON NORTHERN v. VAUGHN              16113
   [6] Finally, the district court’s order “resolve[d] an impor-
tant issue completely separate from the merits of the action.”
See Coopers & Lybrand, 437 U.S. at 468. Courts have gener-
ally found that claims of immunity are separate from the mer-
its of the underlying action. See, e.g., Mitchell, 472 U.S. at
527-28; P.R. Aqueduct & Sewer Auth., 506 U.S. at 145; Com-
pania Mexicana de Aviacion, S.A. v. U.S. Dist. Court for the
Cent. Dist. of Cal., 859 F.2d 1354, 1358 (9th Cir. 1988);
Osage Tribal Council, 187 F.3d at 1180 (holding that whether
the Safe Drinking Water Act abrogated the tribe’s immunity
is “distinct from the underlying merits” of whether the tribe
violated the plaintiff’s whistle blower rights under the Act).
Likewise, the issue in this case, whether the tribal officials are
subject to suit under the doctrine of Ex Parte Young, is sepa-
rate from the underlying merits of BNSF’s claim that the tax
ordinance cannot be enforced against its right-of-way through
the Reservation. See Verizon Md., Inc. v. Pub. Serv. Comm’n
of Md., 535 U.S. 635, 645-46 (2002) (holding that “the
inquiry into whether suit lies under Ex Parte Young does not
include an analysis of the merits of the claim”).

   BNSF argues that interlocutory review is inappropriate
because the district court did not resolve an “important issue”
completely separate from the merits of the action, but rather
applied settled precedent to determine that, under the doctrine
of Ex Parte Young, the tribal officials are not immune from
suit. BNSF cites Nixon v. Fitzgerald, 457 U.S. 731 (1982),
and In re Kemble, 776 F.2d 802 (9th Cir. 1985), for the propo-
sition that an issue is important only if it involves a “serious
and unsettled” question of law. The “serious and unsettled”
language BNSF cites does not define when an issue is impor-
tant under this Cohen factor. Rather, it is a completely sepa-
rate consideration, which is not normally cited as one of the
elements of the collateral order doctrine. See 15A Charles
Alan Wright et al., Federal Practice and Procedure § 3911
(2007).

  [7] There is simply no requirement that the argument on
appeal be novel. See Schwartzman v. Valenzuela, 846 F.2d
16114          BURLINGTON NORTHERN v. VAUGHN
1209, 1210 (9th Cir. 1988) (“[T]he Supreme Court has autho-
rized limited appellate review of a denial at the pretrial stage
of a defense of immunity. State government defendants appar-
ently now deem it mandatory to bring these appeals from any
adverse ruling, no matter how clearly correct the trial court’s
decision.” (citations omitted) (emphasis added)). We think the
issue of tribal official immunity is analogous. The fact that the
district court applied settled law to determine whether immu-
nity barred BNSF’s suit does not prevent interlocutory
review.

   [8] BNSF also contends that the tribal officials, by raising
factual issues regarding ripeness and standing, have created
an “evidence sufficiency” claim, which is not appealable.
BNSF is correct that denial of an immunity claim is appeal-
able on an interlocutory basis only to the extent that it turns
on an issue of law. Johnson v. Jones, 515 U.S. 304, 313
(1995). However, the district court’s order denying the tribal
officials’ motion to dismiss on the basis of tribal immunity
did not involve a determination that genuine issues of material
fact existed for trial, as was the case in Johnson. See id.;
Armendariz v. Penman, 75 F.3d 1311, 1316-17 (9th Cir.
1996). Rather, the district court held that under Ninth Circuit
precedent BNSF’s suit could proceed because “suits against
tribal officers for prospective relief are not barred by sover-
eign immunity.”

   [9] This is not the type of evidence sufficiency claim that
falls outside the collateral order doctrine. Verizon Md., Inc.,
535 U.S. at 645 (“In determining whether the doctrine of Ex
Parte Young avoids [a sovereign immunity] bar to suit, a
court need only conduct a ‘straightforward inquiry into
whether [the] complaint alleges an ongoing violation of fed-
eral law and seeks relief properly characterized as prospec-
tive.’ ” (citation omitted) (second alteration in the original));
Mitchell, 472 U.S. at 528 (“An appellate court reviewing the
denial of the defendant’s claim of immunity need not consider
the correctness of the plaintiff’s version of the facts, nor even
                BURLINGTON NORTHERN v. VAUGHN              16115
determine whether the plaintiff’s allegations actually state a
claim.”).

   [10] We join the Tenth and Eleventh Circuits in holding
that denial of a claim of tribal sovereign immunity is immedi-
ately appealable under the collateral order doctrine. We there-
fore turn to whether the district court properly determined that
BNSF’s suit was not barred by tribal sovereign immunity.

                                B

   Issues of tribal sovereign immunity are reviewed de novo.
Linneen v. Gila River Indian Cmty., 276 F.3d 489, 492 (9th
Cir. 2002). Absent congressional abrogation or explicit
waiver, sovereign immunity bars suit against an Indian tribe
in federal court. Kiowa Tribe of Okla., 523 U.S. at 754. This
immunity protects tribal officials acting within the scope of
their valid authority. Hardin v. White Mountain Apache Tribe,
779 F.2d 476, 479-80 (9th Cir. 1985).

   [11] Under the doctrine of Ex Parte Young, immunity does
not extend to officials acting pursuant to an allegedly uncon-
stitutional statute. 209 U.S. 123, 155-56 (1908) (holding that
Eleventh Amendment immunity was not a bar to suit against
the state’s Attorney General to enjoin him from enforcing a
law that the plaintiffs alleged violated the Due Process Clause
of the Fourteenth Amendment). This doctrine has been
extended to tribal officials sued in their official capacity such
that “tribal sovereign immunity does not bar a suit for pro-
spective relief against tribal officers allegedly acting in viola-
tion of federal law.” Burlington N. R.R. Co. v. Blackfeet
Tribe, 924 F.2d 899, 901 (9th Cir. 1991), overruled on other
grounds by Big Horn County Elec. Coop., Inc. v. Adams, 219
F.3d 944, 953 (9th Cir. 2000).

   [12] In determining whether Ex Parte Young is applicable
to overcome the tribal officials’ claim of immunity, the rele-
vant inquiry is only whether BNSF has alleged an ongoing
16116             BURLINGTON NORTHERN v. VAUGHN
violation of federal law and seeks prospective relief. See Veri-
zon Md., Inc., 535 U.S. at 645-46. Clearly it has done so.
BNSF’s complaint states that “Defendants have acted, have
threatened to act, or may act under the purported authority of
the Tribe, to the injury of BNSF and in violation of federal
law and in excess of federal limitations placed on the power
of the Defendants” by seeking to enforce an unauthorized tax
against BNSF that the Tribe lacks the jurisdiction to impose.
Compl. ¶ 5. BNSF seeks a declaration that the tax is invalid
as applied to its right-of-way and a permanent injunction pro-
hibiting the tribal officials from enforcing the tax against it.
Compl. ¶ 1. This is clearly the type of suit that is permissible
under the doctrine of Ex Parte Young.

   The tribal officials contend that Ex Parte Young does not
apply because the officials “have taken no actions in violation
of federal law and BNSF failed to prove that tribal officials
intend to take such action.” First, as noted above, BNSF is not
required to “prove” anything; it is sufficient that the railroad
has alleged a violation of federal law. Also, the requirement
that the violation of federal law be “ongoing” does not require
BNSF to show that the tribal officials have enforced the chal-
lenged statute. See Wilbur v. Locke, 423 F.3d 1101, 1104-05,
1111 (9th Cir. 2005) (holding that Eleventh Amendment
immunity did not bar suit against state officials where “the
complaint alleged that the challenged statutes authorize the
state to enter into agreements which violate federal law”
(emphasis added)); Nat’l Audubon Soc’y, Inc. v. Davis, 307
F.3d 835, 846-47 (9th Cir. 2002) (rejecting defendants’ argu-
ment that “the Ex Parte Young exception ‘require[s] a genuine
threat of enforcement by a state official before a federal court’
can hear a party’s claims”).2
  2
   Like the defendants in National Audubon Society, the tribal officials
here improperly seek to engraft Article III standing and prudential ripeness
considerations onto the Ex Parte Young analysis. Because these arguments
were not properly raised on appeal or before the district court, we do not
address them here.
                  BURLINGTON NORTHERN v. VAUGHN                      16117
   [13] Although enforcement need not be imminent, the
named officials must have “the requisite enforcement connec-
tion to” the challenged law for the Ex Parte Young exception
to apply. See Nat’l Audubon Soc’y, Inc., 307 F.3d at 847. We
recognize the long history of efforts by the Tribe to impose
and collect taxes on the railroad that resulted in a previous
settlement. Easter is allegedly responsible for administering
and collecting the challenged tax, and has already transmitted
tax registration forms to BNSF, the first step in seeking to
impose and collect more taxes. Because BNSF has alleged
that Easter has “direct authority over and principal responsi-
bility for enforcing” the tax, the Ex Parte Young exception
applies and tribal immunity does not bar suit against her. See
id. at 847. Charles Vaughn, the Tribal Chairman, is responsi-
ble for exercising executive authority over the Tribe. BNSF
has not alleged that Vaughn is in any way responsible for
enforcing the tax. Therefore the Ex Parte Young exception
does not apply to Vaughn and suit against him is barred by
tribal sovereign immunity. See id.

  [14] We therefore affirm the district court’s denial of the
motion to dismiss with regard to Easter. We reverse with
regard to the court’s ruling against Vaughn; his motion to dis-
miss should have been granted.

                                    III

  The exception to the final judgment rule for collateral
orders does not give a court jurisdiction over every claim or
defense addressed by the district court’s order. Instead, we
must be able to exercise jurisdiction over each issue indepen-
dently. See Swint v. Chambers County Comm’n, 514 U.S. 35,
49 (1995). The tribal officials argue that we should exercise
pendent appellate jurisdiction to review whether the district
court properly denied their motion to dismiss for failure to
exhaust tribal remedies.3
  3
   We do not determine whether exhaustion of tribal remedies is a collat-
eral order subject to interlocutory review under Cohen. The tribal officials
16118              BURLINGTON NORTHERN v. VAUGHN
   [15] A court may exercise pendent appellate jurisdiction
over rulings that do not independently qualify for interlocu-
tory review only if the rulings are inextricably intertwined
with, or necessary to ensure meaningful review of, decisions
that are properly before the court on interlocutory appeal.
Swint, 514 U.S. at 51; Poulos v. Caesars World, Inc., 379
F.3d 654, 668 (9th Cir. 2004). These requirements are nar-
rowly construed, setting “a very high bar” for the exercise of
pendent appellate jurisdiction. Poulos, 379 F.3d at 669. That
bar is not met here.

   First, the tribal officials’ sovereign immunity and exhaus-
tion of tribal remedies claims are not inextricably intertwined.
A court may exercise pendent appellate jurisdiction only if it
“must decide the pendent issue in order to review the claims
properly raised on interlocutory appeal” or if “resolution of
the issue properly raised on interlocutory appeal necessarily
resolves the pendent issue.” Id. (quotation marks omitted).
Issues are not inextricably intertwined if different legal stan-
dards apply to each issue. Id. The tribal sovereign immunity
claim turns on whether BNSF has alleged a continuing viola-
tion of federal law and seeks prospective relief. The exhaus-
tion of tribal remedies claim requires the court to analyze
whether there is a colorable claim of tribal court jurisdiction.
These issues “turn on wholly different factors,” and therefore
are not inextricably intertwined. See, e.g., id. at 670 (primary
jurisdiction and class certification issues not inextricably
intertwined); Meredith v. Oregon, 321 F.3d 807, 815 (9th Cir.

waived this argument by raising it for the first time in their reply brief. See
Singh v. Ashcroft, 361 F.3d 1152, 1157 n.3 (9th Cir. 2004). The tribal offi-
cials also discussed for the first time in their reply brief pendent appellate
jurisdiction as a basis for jurisdiction over the exhaustion of tribal reme-
dies claim. However, pendent appellate jurisdiction was discussed by
BNSF in its answering brief, so that issue has been joined and we may
consider it. See In re Riverside-Linden Inv. Co., 945 F.2d 320, 324 (9th
Cir. 1991) (“We have discretion to review an issue not raised by appellant,
however, when it is raised in the appellee’s brief.”).
                   BURLINGTON NORTHERN v. VAUGHN                       16119
2003) (Younger abstention and preliminary injunction not
inextricably intertwined); Stewart v. Oklahoma, 292 F.3d
1257, 1260 (10th Cir. 2002) (Eleventh Amendment immunity
and exhaustion of administrative remedies not inextricably
intertwined).

   [16] Likewise, exercising pendent appellate jurisdiction
where the pendent claim shares only a “tangential relationship
to the decision properly before [the court] on interlocutory
appeal,” is not “necessary to ensure meaningful review” of
that decision. Poulos, 379 F.3d at 669. In Meredith v. Oregon,
the court found that review of the pendent Younger abstention
decision was necessary to provide meaningful review of the
preliminary injunction decision because “if the district court
is required to abstain under Younger and dismiss the suit, then
it has no authority to rule on a party’s motion for a prelimi-
nary injunction.” 321 F.3d at 816. Similar considerations are
not present in this case. Determination of whether the tribal
court has jurisdiction, and thus exhaustion is required, is not
necessary to provide meaningful review of the tribal officials’
claim that they are completely immune from suit in federal
court. Because this is not one of the rare instances in which
pendent appellate jurisdiction is appropriate, the remaining
claims on appeal are dismissed for lack of jurisdiction.4

                                     IV

  Under the collateral order doctrine, we have jurisdiction
over the denial of the tribal officials’ motion to dismiss on
  4
    The district court’s holding that exhaustion of tribal remedies was not
required was based on its finding that the tribal officials could not make
a colorable claim of tribal court jurisdiction. The tribal officials argue that
the district court erred in so finding. Because we do not have interlocutory
jurisdiction over the issue of exhaustion of tribal remedies at this stage of
the case, we do not yet have jurisdiction to review the district court’s find-
ing regarding the scope of the tribal court’s jurisdiction and we do not
decide now whether this finding was correct. That issue may be consid-
ered if necessary on appeal from any final judgment below.
16120          BURLINGTON NORTHERN v. VAUGHN
tribal sovereign immunity grounds. Reviewing the claim on
the merits, the Ex Parte Young exception applies to Easter,
who is allegedly responsible for enforcing the challenged tax,
and tribal sovereign immunity is not a bar to suit against her.
We therefore affirm the district court’s denial of the motion
to dismiss as to Easter. The exception does not apply, how-
ever, to the suit against Chairman Vaughn because BNSF has
not alleged that he is connected to enforcement of the tax, and
we reverse that part of the district court’s order. Finally, we
elect not to exercise pendent appellate jurisdiction over the
exhaustion of tribal remedies claim as it is not inextricably
intertwined with, or necessary to ensure meaningful review on
interlocutory appeal, of the tribal sovereign immunity claim.
The remainder of the appeal is therefore dismissed. Each
party shall bear its own costs on appeal.

  AFFIRMED in part; REVERSED in part; DISMISSED in
part.
