Established in 1861 with the South Platte River as its west border, Douglas County encompasses rolling prairie and pine-timbered hills. The mountainous southwest quadrant lies within the Pike National Forest. A once rural county originally known for its Black Forest pineries and its rhyolite quarries, Douglas supplied lumber and a popular building stone for the nineteenth-century Front Range building boom.
Silas W. Madge, while digging around his mesa-top ranch two miles south of Castle Rock, found hard, pink and gray lava rock approximating granite. To capitalize on this large rhyolite formation, he opened a quarry in 1872 and arranged to have the Denver & Rio Grande Railroad build a spur line. Rhyolite soon became Colorado's favorite building stone, especially in towns along the railroad. Reopened for restoration projects, the original quarry is now operating as the Hallet Quarry. When the Santa Fe Railroad arrived in Castle Rock in 1889, it opened the Santa Fe Quarry on a nearby mesa top. The O'Brien (1881) and other quarries also produced the fine-grained volcanic stone, colored from near white to pink, gray, and tan. This stone is very strong for its weight and, since it hardens with exposure to air, weathers well. It appears in many notable Colorado landmarks, including Denver's Trinity Methodist Church and Union Station. The growing popularity of Portland cement and terracotta closed these quarries in the first decade of the twentieth century.
Since World War II, thoroughbred horse and cattle ranching, dairying, clay mining, explosives manufacture, and the Martin Marietta missile plant have been major employers. Sandwiched between the expanding metropolitan areas of Denver and Colorado Springs, Douglas became the second fastest-growing county in the United States during the 1990s.
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