ABSTRACT Mount Diablo Coalfield was the largest producer of coal in California from the 1860s to 1906. The now-depleted coalfield is located on the northeast limb of the Mount Diablo anticline. The mineable coal seams occur in the Middle Eocene Domengine Formation, which is predominantly composed of quartz-rich sandstone with several thin coal seams. As many as 26 mine operations were established to mine the coal, and it has been estimated that the total production exceeded 4 million tons. The coal fueled the industrial growth of the major cities of northern California. The mines closed at the turn of the nineteenth century as competition from better coals from Washington Territory and overseas entered the market. After coal mining was abandoned, sand operations were established in the early and mid-twentieth century to mine the silica-rich sandstone. The extraction methods used for sand were underground room-and-pillar mining and surface open-pit mining. The high-quality sand was used widely in the production of pottery and glass, and in foundries. Previous studies have interpreted the environment of deposition of these quartz-rich sandstone and coal deposits as barrier island with tidal channels or delta, tidal shelf, and marsh complexes along a north-south–trending shoreline. However, the excellent exposures in the sand mines display abundant evidence for their deposition in a fluvial/estuarine system. Their regional distribution indicates that they were deposited in a northeast-southwest–trending incised-valley system formed by fluvial incision during a lowstand. The incised valley was filled with fluvial and estuarine deposits made up of quartz-rich sand brought in by streams that flowed westward from the Sierra Nevada.

Abstract The story of UK onshore exploration goes back to the days of World War I and was prompted by the increasing use of oil for the war effort. The war was drawing to a close as the campaign commenced in 1918. The UK government sponsored the drilling with a budget of £1 000 000 and the work was undertaken by S. Pearson & Sons, a UK engineering company owned by Lord Cowdray (Weetman Pearson). Pearson also had oil interests and he owned the Mexican Eagle Company that had had exploration success in Mexico. Pearson hired a team of American geologists to select suitable drilling locations in the UK. The Carboniferous rocks in the area surrounding the Derbyshire Dome in England and the Midland Valley in Scotland were chosen because of their similarity to the oil-producing areas of Pennsylvania and West Virginia in the USA. Eleven wells were sunk: seven in Derbyshire, two in North Staffordshire and two in Scotland. The first well to be spudded was at Hardstoft in Derbyshire in October 1918 and it was also the first oil discovery. The geological reasoning behind the selection of the drilling sites will be compared with the actual results from 1918–22.