OF-19-05 Geologic Map of the Hells Kitchen Quadrangle, Delta and Mesa Counties, Colorado

The Hells Kitchen quadrangle lies in Delta and Mesa Counties, Colorado, approximately 13 mi (21 km) north of Delta. The map area is characterized by a high mesa (Grand Mesa) formed by the Miocene eruption of the Grand Mesa Volcanic Field (GMVF), epeirogenic uplift, and topographic inversion. The lava flows of the GMVF formed two westward lobes divided by the Kannah Creek Basin: the Palisade Lobe flowed to the west, and the Flowing Park Lobe (FPL) to the southwest. The Hells Kitchen quadrangle includes the northeastern half of the FPL to Kannah Creek and a sliver of the Palisade Lobe near Carson Lake, near where the two lobes diverge. Grand Mesa rises a mile (1.6 km) in elevation above the confluence of the Gunnison and Colorado rivers in Grand Junction and is a major physiographic landmark of western Colorado. In the map area, the annual precipitation ranges from 36 inches (91 cm) on Grand Mesa where alpine forest is predominant, to 12 inches (31 cm) at the lowermost flank of the map area where semi-arid to arid pinyon-juniper woodlands and Adobe Badlands occur. The Cenozoic and Late Cretaceous evolution of western Colorado is recorded in the terrestrial formations exposed in the map area. The basal unit exposed in the map area are the upper members of the Late Cretaceous Mancos Shale. This very thick, marine shale was deposited during the transgression of the Cretaceous Western Interior Seaway (CWIS). Regressive and transgressive sequences of the western shoreline of the CWIS formed the Iles Formation in shoreface and nearshore environments. Of note is the 100-ft (30-m) high gray-white cliffs of the Rollins Sandstone Member that is a prominent stratigraphic marker bed. As the paleo shoreline regressed to the east, Late Cretaceous Williams Fork Formation formed from broad floodplain environments and the deposition of sand, mud, and swamp sediments transported from west and southwest sources. Commercial coal deposits in the Cameo-Wheeler coal zone were formed. Uplifts during the Laramide orogeny, of latest Cretaceous and Paleogene ages, existed along the Southern Rocky Mountain orogenic belt in Central Colorado. The resultant erosion from these eastern highlands shed a thin unit of sandstone with coarse gravel and cobbles that would become the conglomerates of the Ohio Creek Formation, followed by thick packages of clastic sediments to the west that would become the Paleogene Wasatch Formation. The differentiation of closed, intermontane Paleogene basins formed large freshwater lakes. Lacustrine and lake shoreface sediments would become the Paleogene Green River Formation (Franczyk and others, 1992). Eventual integration and establishment of the westward drainage network of the paleo Colorado River Basin occurred on a topographically subdued Late Miocene ground surface. The eruption of Neogene GMVF basaltic lava flowed onto this surface. Later Neogene epeirogenic uplift of the Colorado Plateau, and concurrent to early Quaternary river incision by the Colorado River and its Gunnison River tributary caused several thousand feet of regional topographic lowering, possible erosional-isostatic rebound, and topographic inversion of the more resistant GMVF basalt to form Grand Mesa. Later Quaternary events include the Pleistocene glacial epochs, and mass wasting of the flanks of Grand Mesa that continues today.