By: Grant C. Willis and Janice M. Hayden
The Santa Clara 7.5′ quadrangle is in the northwestern part of the St. George basin in southwestern Utah, and includes Santa Clara and Ivins Cities, and colorful Red Mountain and Snow Canyon State Park. Movement on an underlying thrust fault created a variety of faults, joints, deformation shear bands, and brecciated rock in Triassic and Jurassic strata in many areas. Remnants of six Quaternary basalt flows cap ridges and benches, forming classic inverted valleys, and form lava cascades in Snow Canyon State Park. The young Santa Clara flow cascaded through Snow Canyon and flooded across broad benches, forming scenic black terrain that contrasts sharply with red-brown to near-white sandstone cliffs. Landslides, rock falls, swelling clays, and other geology and related flooding and debris flow hazards have caused extensive damage in recent years and present increasing challenges as growth and development continue. “Blue Clay” of the Chinle Formation has been at the root of significant damage to roads, buildings, and infrastructure.