The La Sal Mountains, near Moab in southeastern Utah, are laccoliths formed when upwelling magma intruded into and bulged the overlying sedimentary rock layers upward. The magma did not reach the surface, but subsequent erosion of the softer sedimentary rocks exposed the peak-forming igneous rocks that rise above the surrounding landscape.
A geologist examines a sequence of Early Cretaceous-aged paleosols (ancient soils) in the Yellow Cat Member of the Cedar Mountain Formation. Many dinosaur fossils are found in these rocks, and the study of paleosols can provide valuable
information about the environments in which these dinosaurs lived.
Arches National Park, Grand County, Utah
Photographer: Michael Vanden Berg
A small window in the Slick Rock Member of the Entrada Sandstone frames a view of Utah’s most famous landform, Delicate Arch. The arch is composed of Jurassic-aged sandstone including the Slick Rock Member (base and pedestals) and Moab Member of the Curtis Formation (bridge). In the distance, Oligocene-aged igneous rock forms the snow-covered La Sal Mountains.
Slickrock Trail near Moab, Grand County, Utah
Photographer: Jim Davis
Giant weathering pits or potholes like this one (about 16 feet across at the bottom) in the Jurassic-age Navajo Sandstone typically form along fractures and joints atop fins, knolls, and rounded domes. Potholes are created through a combination of physical, chemical, and biological processes that weather and erode the rock and are home to a remarkable array of ancient aquatic organisms.