 The museum also has a substantial collection of manuscripts by Cherokee principal chief John Ross and Choctaw Chief Peter Pitchlynn.The Helmerich Center for American Research at Gilcrease Museum is an archival center on the museum grounds that permits researchers to access the many rare documents housed at the museum.These items may only be used in the Reading Room, an environmentally controlled, secure area, designed to protect them against loss or damage.The documents themselves are stored in a hardened concrete structure that was designed to protect them from severe weather events like tornadoes.