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Comprehensive Plan Conservation Element EXISTING CONDITIONS Abiotic Features Geology The land surface of Indian River County is underlain by nearly 10,000 feet of sedimentary rocks (carbonates, sands, and clays) which overlay a "basement" complex of igneous and metamorphic rocks. Within the upper 1,000 feet, sediments consist of limestone, dolomite, sand, clay, and shell beds. These sediments are comprised mainly of unconsolidated clastic material (sand and clay) termed the "clastic zone". This area is known as the Tamiami formation or the Fort Thompson formation. The Anastasia formation, found along the coastal area, consists of quartz sand and shell material (Coquina). Within 200 feet of the surface lies the surficial aquifer system. Overlying sediments are predominantly composed of clastic material (sand and clay) and contain the surficial aquifer. Below the surficial aquifer lies the Hawthorn formation. This formation consists of inter bedded limestone, dolomite, sand, and clay, and is about 250 feet thick in Indian River County. The formation acts as a confining layer between the Floridan and surficial aquifers. The Floridan aquifer system includes the Oldsmar, Lake City and Avon Park limestone formations, the Ocala Group, and the Undifferentiated Oligocene Rock layer. While the Lake City and Oldsmar limestone formations are found over 1,000 feet deep, the Avon Park formation consists of limestone and dolomite, and reaches a thickness of up to 250 feet. Immediately overlying the Avon Park formation is the Ocala Group, consisting of the Inglis, Williston, and Crystal River formations, all composed of limestone. The General Geologic Profile of Indian River County is depicted in Figures 8.1 and 8.2. • Commercially valuable minerals In Indian River County, minerals mined for commercial value are limited to sand and gravel. Historically, the primary location for sand mining in the county was the Atlantic Coastal Sand Ridge, generally found parallel and proximate to U.S. Highway #1. Figure 8.3 depicts the location of active mining operations in Indian River County as of July 2008. Locally, the predominant use of sand has been for construction purposes, generally for fill related to building construction in low lying areas and locations where on-site disposal (septic) systems are installed. In the past, sand mined from the ridge has been used to renourish the beach area south of Sebastian Inlet. Due to past mining operations, most of the mining potential of the Atlantic Coastal Sand Ridge has been depleted. As a result, mining operations now occur in areas west of the U.S. Highway #1 corridor. Community Development Department Indian River County 2