 Following the onset of a severe drought, most Chacoans emigrated from the canyon by 1140; by 1250 Chetro Ketl's last inhabitants had vacated the structure.The great house was rediscovered in 1823 by the Mexican governor of New Mexico, José Antonio Vizcarra, and in 1849 Lieutenant James Simpson of the United States Army Corps of Engineers documented the major ruins in Chaco Canyon.Edgar L. Hewett, the director of the first archeological field school in the canyon, conducted excavations of Chetro Ketl during 1920 and 1921, and again between 1929 and 1935.