The Tallgrass Prairie originally covered portions of 14 states and 142 million acres, and was one of North America's largest ecosystems. It exists now only in the Flint Hills of Oklahoma and Kansas. The Tallgrass Prairie Preserve was purchased in 1989 by the Nature Conservancy and consists of the 30,000 acre Barnard Ranch, and approximately 9,000 more acres.
From Tulsa, take Highway 11 North to Pawhuska. The Preserve is just north and west of Pawhuska. Once in Pawhuska, just follow the signs through town where the scenic tour drive actually begins. The drive is approximately 35 miles and lasts about two hours through the preserve.
Source: The Nature Conservancy website.