Here are the materials in Fletcher v. United States:

CA10 Opinion

Fletcher Opening Brief

Interior Answer Brief

Fletcher Reply Brief

An excerpt:

After settlers displaced the Osage Nation from its native lands, the federal government shunted the tribe onto the open prairie in Indian Territory, part of what later became the State of Oklahoma. At the time, the government had no idea those grasslands were to prove a great deal more fertile than they appeared. Only years later did the Osages’ mammoth reserves of oil and gas make themselves known. When that happened, the federal government appropriated for itself the role of trustee, overseeing the collection of royalty income and its distribution to tribal members. That role continues to this day. In  this lawsuit, tribal members seek an accounting to determine whether the federal  government has fulfilled the fiduciary obligations it chose to assume. The district court
dismissed the tribal members’ claims. We reverse.

Lower court materials here and here.