The Greasewood oil field is located in Secs. 13 and 24, T. 6 N., R. 61 W., at the eastern boundary of Weld County, Colorado.

The early geology of the area by the Hayden Survey was concerned with the stratigraphy in relation to other areas of the Great Plains. The writer was engaged by the Greeley Chamber of Commerce to make a reconnaissance of the oil possibilities of the county in 1923, which study resulted in the discovery of the Greasewood anticline. Later work under the direction of R. D. George resulted in the drilling of a test well, which discovered oil in the Greasewood sandstone on October 10, 1930.

Surface rocks of the area belong to the Laramie and Fox Hills (Cretaceous) formations, and oil is produced from the lower part of the Cretaceous series at depths of 6,639-6,683 feet. The producing area is very small and the reservoir rocks are very erratic. Only three wells out of nine drilled in the immediate area were commercial producers. One well is still producing 15-30 barrels of oil per day, flowing naturally.

Accumulation of oil in the Greasewood sandstone is due to a combination of stratigraphic and structural factors.