Mantle's Cave is a cliff alcove in Dinosaur National Monument in Moffat County, Colorado. Located in the Castle Park region of the park, it is the largest rock shelter in the area. It was discovered before 1921 by local ranchers, Mr. and Mrs. Charles Mantle. Mrs. Mantle is reported to have done some excavation of the site, followed up by the Penrose-Taylor expedition of 1933 from Colorado College and the Fountain Valley School, which designated the site "Cave One." The site is a significant resource for the Fremont culture and is among the best resources in northwestern Colorado. Excavations in the 1930s and 1940s yielded significant material on the Fremont people and their relationship to the later Ancestral Puebloans.