Here are the materials in Rincon Mushroom Corp. v. Mazzetti:
Lower court materials here.
An excerpt from the Ninth Circuit opinion:
The Tribe argues that the non-member fee land at issue could potentially contaminate the Tribe’s water supply, or exacerbate a future fire that might damage the Rincon Casino. However, these possibilities do not fall within Montana’s second exception, which requires actual actions that have significantly impacted the tribe. Compare id. at 341 (“The sale of formerly Indian-owned fee land to a third party . . . cannot fairly be called ‘catastrophic’ for tribal self-government. . . .”) (citation omitted); and Strate v. A-1 Contractors, 520 U.S. 438, 458-59 (1997) (ruling that tribal court jurisdiction over tort suits is not “needed to preserve the right of reservation Indians to make their own laws and be ruled by them”) (citation and internal quotation marks omitted), with Elliott, 566 F.3d at 844, 849-50 (holding that the tribal court had colorable jurisdiction where a non-Indian started a forest fire on reservation land).
To hold that the potential threats of harm presented on this record give rise to tribal jurisdiction under Montana’s second exception would allow the exception to swallow the rule; any property within the Rincon Reservation faces similar potential threats. See Plains Commerce, 554 U.S. at 330. Because the potential threats did not create a plausible basis for tribal court jurisdiction, the district court erred when it dismissed RMCA’s Complaint for failure to exhaust tribal remedies. See Elliott, 566 F.3d at 848.
Compare that language to the lower court’s description of the same allegation:
Defendants have submitted evidence indicating that conduct on Plaintiff’s property “pose direct threats to the Tribe’s groundwater resources.” (Minjares Decl. ¶ 29, Doc. # 52). Defendants also have submitted evidence that “[c]onditions on the Subject Property during the  Poomacha Fire contributed to the spread of wildfire from that property to Tribal lands across the street on which the Casino is located.” (Mazzetti Decl. ¶ 15, Doc. # 17-2). Although Plaintiff disputes this evidence, Defendants have shown that conduct on Plaintiff’s property plausibly could threaten the Tribe’s groundwater resources and could contribute to the spread of wildfires on the reservation. This showing is sufficient to require exhaustion, given the relief requested by the first two counts of the Complaint.