MARTIN CREEK. Martin Creek, also known as Deep Creek, rises three miles north of Fly Gap in northeastern Mason County (at 30°52' N, 99°04' W). Intermittent at places in its upper and lower reaches, the stream flows southeast for sixteen miles, running through sandy beds as it nears its mouth on the Llano River, one mile west of the Llano county line (at 30°43' N, 98°59' W). The stream rises in the limestone hills on the eastern edge of the Edwards Plateau and crosses an area of the Llano basin characterized by flat to rolling terrain surfaced by deep to shallow sandy and clayey loams. Vegetation consists chiefly of scrub brush, grasses, and open stands of live oak and mesquite.