CIENEGA MOUNTAIN. Cienega Mountain is sixteen miles south of Alpine in western Brewster County (at 30°07' N, 103°39' W). With an elevation of 6,562 feet above sea level, it rises 1,960 feet above State Highway 118, five miles to the east. The core of the mountain is a large intrusive body of the Tertiary period, between 2 million and 66 million years old. The region's shallow, stony soils support scrub brush and grasses.