The purpose of this map is to describe the geology, mineral and ground-water resource potential, and geologic hazards of this 7.5-minute quadrangle located east of Grand Junction, Colorado. It adds to our geologic coverage of the Grand Mesa area. Includes 2 plates and GIS data in a single zip file. Digital ZIP download. OF-19-08D
From Plate 2, Physiographic and Geologic Setting:
The Grand Mesa of western Colorado is one of the world’s largest flat-topped mountains, reaching 11,319 ft (3,450 m) and extending over 500 mi2 (1,300 km2). The topography of the Grand Mesa area formed in response to late Cenozoic downcutting of the upper Colorado River system. The Grand Mesa is an example of topographic inversion, where c. 10 Ma valley-filling basalt flows of the Grand Mesa Volcanic Field (GMVF) are now positioned on the watershed divide between the Colorado and Gunnison Rivers, more than 5,900 ft (1,800 m) above adjacent valley bottoms. The Mesa Lakes quadrangle straddles the border between Mesa and Delta counties. The center point of the quadrangle is 26 mi (41.8 km) east of Grand Junction, Colorado. Grand Mesa is dual-lobed and has a “Y” shaped outline. Crag Crest (east of the quadrangle) forms the stem and the Palisade and Flowing Park lobes form the north and south branches, respectively. The quadrangle includes the east-central portion of Grand Mesa, the eastern section of the Palisade lobe and the northernmost region of the Flowing Park lobe. The geology and geomorphology across the top of the mesa is dominated by basalt outcrops overlain by thin accumulations of glacial deposits and associated landforms. In contrast, the topography to the north and south of the mesa rim is in large part controlled by mass wasting processes and associated deposits initiated in underlying Neogene-to-Paleogene continental sedimentary rocks. Intact exposures of these Cenozoic sedimentary rocks are uncommon across the quadrangle.