Oil Creek—site of the first oil well in the west—second place in the United States to produce petroleum from wells. In 1862 ... A. M. Cassedy drilled an oil well 50 feet deep. By February, 1863, production was one barrel a day. Later, several thousand gallons of petroleum were produced by primitive methods, and kerosene and lubricating oil were shipped by ox team as far as Denver and Santa Fe. About twenty miles to the southeast, near Florence, the Cretaceous Pierre shales were drilled in 1876. Oil was found in a system of intersecting fractures and joints. Some of the early wells in the Florence field are still producing, making this Colorado’s oldest and longest producing field. It has yielded more than 10,000,000 barrels of oil. Small quantities of oil have been produced near Boulder since about 1900, also from Pierre sandstones and shales. In this area, wells were located by “dowsing” or “witching,” as was fashionable at the time. Several old rigs can be seen near Boulder Reservoir. As at Florence, oil has been trapped in fractures of otherwise dense and impervious shale. Some gas is produced and is used by local farms. More recently, oil was found far beneath the surface in the northern part of the Prairie Province. Here, in the Denver Basin, oil is produced from several levels in the Dakota Sandstone. The oil has accumulated in lenses of beach sand deposited along the shoreline of the Cretaceous sea. The general trend of the shoreline, and of the oil fields, is northeast-southwest. The shore appears to have been similar to Georgia’s present coastline: a swampy tidal zone separated from open sea by lagoons, sandy bars, and clean sand beaches. Individual oil pools in the Denver Basin are small, but there are many of them; they lie nearly a mile below the surface, under much of Morgan and Logan Counties and adjacent parts of Nebraska. Exploratory and development drilling keeps total oil production at about 50,000 barrels a day. Oil and gas produced here is piped to Denver and other Colorado cities. In southeastern Colorado, oil and gas occur in late Paleozoic limestones and sandstones similar to those which outcrop at the edge of the Wet Mountains. Prospecting by geophysical methods and by drilling has revealed several small, rich accumulations, one of which is thought to contain about 30,000,000 barrels of oil.