In 1938, the Mississippi Geological Survey in cooperation with the W.P.A. undertook a geological survey in ten counties. Assistant state geologist Fredric F. Mellen supervised several county surveys in search of good ceramic clays. Mellen observed several indications of geologic structure. In February 1939 near Tinsley in Yazoo County, he noted an outcrop of Moodys Branch Marl at an elevation 250 feet above its normal position. Based on his training in physical, historical and paleontological geology, he concluded the presence of a structure favorable to the accumulation of gas and oil.
A press release on April 12, 1939 announced the discovery and suggested that it warranted further geologic study and seismographic exploration. After the release Union Producing Company (United Gas, now Pennzoil) already active in western Mississippi assembled a lease block near Tinsley and began drilling on July 8. On August 29, 1939 the well struck oil. Union Producing Company's G.C. Woodruff No. 1 was officially completed on September 5, 1939, the first commercial oil well in Mississippi and the discovery well of Tinsley oil field, the largest oil field in the southeast.
All major oil companies moved support personnel into the state, geologists, landperson, geophysicists, engineers, seismic crews, production personnel and drilling crews converged on Mississippi from every section of the country. Since its discovery, 452 producing wells and 42 dry holes have been drilled at Tinsley. New fields were discovered as a result of Tinsley and oil or gas has been found in 42 of the 82 counties. The economic impact of the oil industry on the state has been paramount.
Producing oil and gas fields included: Cranfield, Carthage Point, Bruinsberg, Langsdale, Quitman, Jackson, Heidelberg, Soso, Fayette, Gwinville, Baxterville, Brookhaven, Mallalieu, Pickens, Flora, Hub, Cary, Eucutta, Tinsley and Amory (abandoned).