Great Plains Grasslands Wilderness Act

Great Plains Grasslands Wilderness Act - Establishes the Great Plains Historic Grassland Wilderness Area (the "Area") in North Dakota, South Dakota, and Wyoming, to be managed (with certain exceptions) by the Secretary of Agriculture. Allows the Indian tribe located on a reservation nearest to a grassland that is in the Area to assist in the management of the grassland. Declares that grasslands located within the boundaries of a reservation shall be under the total control of that reservation.

Withdraws, subject to existing rights and treaties with Native American tribes, all Federal lands within the Area from provisions in certain laws, including from the operation of the mineral leasing laws and all forms of entry, appropriation, or disposal under the public land laws.

Directs the Secretary to maintain or restore fish and wildlife populations and their habitats. Provides for the reintroduction of noncommerical American bison into the Area, and forbids hunting of such bison. Prohibits grazing by cattle, sheep, or other commercialized animals in the Area.

Protects tribal rights, and directs the Secretary to permit access for tribes to the Area for traditional cultural and ceremonial purposes.

Directs that a study of certain rivers be conducted to ensure that wildlife in the Area have access to clean drinking water.

Establishes within the Department of the Interior the Office of Native American Wilderness Management. Requires the Director of such Office to coordinate programs that provide assistance to eligible tribal governments in their management of natural environments. Requires the Director to initiate a two-year study of the Area by Indian tribes with the aim of discovering how to restore the grasslands in the Area to their original, natural states as closely as possible.