Grand Mesa (c.50 sq mi/130 sq km), one of the largest flat-topped mesas in the U.S., in Delta and Mesa cos., W Colo.; lies within part of Grand Mesa Natl. Forest. Elev. 10,000 ft/3,048 m. Deposits of coal and oil shale. Volcanic top layer protects the mesa from erosion. Over 200 lakes cover its top, which is 5,000 ft/1,524 m above the surrounding land.