Profile Picture Utah Open Data Portal

created Jan 13 2018

updated Jan 13 2018

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Description

This digital dataset represents the geology of the Santa Clara quadrangle at 1:24,000 scale. The quadrangle is in the northwest part of the St. George basin of southwest Utah and includes the city of Santa Clara in the south part, Snow Canyon State Park in the northeast, and Red Mountain in the northwest. Strata in the quadrangle dip about five to eight degrees northeast on the west flank of the very broad, poorly defined St. George syncline. The Triassic and Jurassic Moenkopi, Chinle, Moenave, and Kayenta Formations form broad northwest-trending swaths across the quadrangle; the youngest formation, the Early Jurassic Navajo Sandstone, forms Red Mountain and Snow Canyon in the northern half of the quadrangle. Strata are allochthonous above a thrust fault that is probably within deeply buried Cambrian rocks and show strong evidence of thrust-related structural deformation. The Navajo Sandstone in particular is cut by large conjugate faults, joints, and deformation shear bands, and is shattered and brecciated in many areas, most noticeably in the Red Mountain area. Some of these structures may be reactivated as basin-and-range normal faults and may be active. Moenkopi strata are locally folded into small anticlines and synclines, the more chaotic of which were caused by dissolution of gypsum beds. Remnants of six Quaternary basaltic (basalt to trachyandesite) flows cap ridges and benches near the east edge of the quadrangle, forming inverted valleys. The distal end the Gunlock flow caps a ridge near the west-central edge of the quadrangle. The approximately 33,000-year-old Santa Clara flow vented from a cinder cone in the northwest corner of the quadrangle and cascaded through Snow Canyon and the Santa Clara City area, and contrasts sharply with the reddish-orange-brown to pale gray Navajo Sandstone to form highly scenic Snow Canyon State Park. The undated but slightly younger Diamond Valley flow vented just outside the quadrangle and ponded in and near the northeast corner. Rapid erosion by the Santa Clara River and tributaries creates scenic rugged topography throughout the quadrangle. A variety of geologic and geology-related hazards present frequent engineering and safety challenges in many areas. Of particular note is smectitic clay of the Chinle Formation. This unit and surficial deposits derived from it are called the “blue clay” by the local community and have caused landslides, swelling soils, and collapsible soils in the southern part of the quadrangle. Other formations and deposits also present challenges that should be considered in any project.

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