The La Rosa field was discovered in September, 1938, as a result of geophysical work preceded by detailed subsurface mapping. There are at present 72 oil wells producing from six separate sands ranging in depth from 5,400 to 6,300 feet, and there are six gas wells which are completed in three different gas sands. The producing area is cut by a normal fault downthrown toward the southeast and the upthrown side produces only gas. The field proper is located on the downthrown side and produces both gas and oil. This field exhibits a type of structure which is common to producing areas in the lower Gulf Coast; that is, an anticlinal fold of low relief on the downthrown and downdip side of a normal fault. Of particular interest is the fact that nearly all structural movement w thin the field occurred previous to the end of Frio deposition and little or no structure is observed in formations younger than the Frio.