The Newcastle quadrangle embraces the quarter of a square degree which lies between parallels 43° 30' and 44° north latitude and meridians 104° and 104° 30' west longitude. It measures approximately 34 1/2 miles from north to south and 25 1/8 from east to west, and its area is 863 4/5 square miles. It lies mainly in the eastern portion of Weston County, Wyo., but includes also a narrow area of western Custer and Pennington counties, S. Dak. The northeastern portion of the quadrangle lies on the slopes of the Black Hills, but the larger part of it belongs to the Great Plains, although these plains are lower here than in the greater part of adjoining portions of Nebraska and Wyoming. The district is drained by branches of the South Branch of Cheyenne River.