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Sector One Chapter 2 - Today <br />The Natural Environment <br />Geology <br />Sector One like much of San Marcos, is traversed by the Balcones Escarpment, an <br />ancient fault line with broken and lifted sedimentary rock and exposed outcrops of <br />Edwards limestone. This area, to the west of Hopkins and Hunter Roads, is hilly and <br />characterized by rocky, shallow soil. Some of the best views in San Marcos are found <br />from homes in the Heritage and Westover Neighborhoods, situated on the escarpment. <br />The southeastern and southern portions of Sector One lie in the Blackland Prairie, an <br />erodable chalk and clay -shale base generally covered by thick clay soils. These soils <br />have a tendency to shrink and swell, a factor to be taken in to account when building. <br />This area is characterized by gently rolling to flat land, with many large trees and <br />significant amounts of open space. <br />Topography <br />Land elevations in Sector One vary from 570 feet above sea level near the intersection of <br />Gravel Street and Jackman Street to 750 feet above sea level near Burt Street, making <br />this sector one of the most picturesque areas of San Marcos. Sector One topography is <br />shown on the Natural Features map, following this section. <br />Edwards Aquifer Zone <br />The Edwards Aquifer is the water - bearing underground network of porous and <br />honeycombed limestone formation of the Edwards Plateau. It is one of the primary <br />sources of water for San Marcos, as well as over 1.5 million other Texans, and is the <br />source of the San Marcos River. The western portion of Sector One, on the escarpment, <br />is located in the recharge zone, an area of fractures, caves and porous limestone, which <br />provides a path for water to run from the surface into the artesian area of the aquifer. The <br />remaining portion of Sector One is located in the transition zone, where faults, fractures, <br />and other geologic features present possible avenues for recharge of surface water into <br />the aquifer. The Edwards Aquifer Recharge Zone boundary is shown on the Natural <br />Features map, following this section. <br />Watersheds <br />A watershed is an area that drains into a river or creek. Portions of Sector One lie in the <br />Purgatory Creek and Willow Springs Creek watersheds. <br />Adopted: September 13, 2004 2 -3 <br />