The Laredo district is in the extreme southern part of Texas and includes five counties: Duval, Jim Hogg, Webb, Starr, and Zapata.
Oil and gas production is obtained from the Fayette, Yegua, and Cook Mountain formations of Eocene age. In general, oil production has been rather disappointing, due to irregular sand conditions, but the presence of commercial quantities of oil at shallow depths in such a large area indicates the possibilities of better production when the proper combination of sand and structural conditions are encountered.
Faulting and sand lensing are the principal factors of the accumulation of oil and gas in this district. Although the major part of the folding and faulting is post-Eocene in age, some movement took place throughout Eocene time. This movement appears to have controlled the position of shore lines at intervals during the Fayette period.
Figures & Tables
Structure of Typical American Oil Fields, Volume I
Modern petroleum geology in the United States had its beginning in the first decade of the 20th Century when the U.S. Geological Survey began mapping the structure of the rocks in and near old fields in order to discover the various types of structural conditions under which oil and gas are trapped. Structural geology has evolved as a branch of the broader science far more rapidly than have methods of mapping the attitude of rocks at the surface. This volume, published in the late 1920s, was designed to afford authoritative and modern descriptions of the structure of typical oil fields in the United States. Each of the 30 fields contained here is described by an author who is intimately familiar with the available data. The relationship of structure at the surface and at depth for different terranes is clearly set forth wherever the strata are not parallel. Fields include: McKittrick, California; Fairport, Kansas; Urania, Louisiana; Artesia, New Mexico; Burbank, Oklahoma; Cabin Creek, West Virginia; and Luling, Texas.