The Balcones Escarpment is a geologic fault zone several miles wide consisting of several faultings, most of which both dip and are downthrown to the east. It extends in a curved line across Texas from Del Rio to the Red River and is visible eastward from Del Rio, where it is about 1,000 feet high, and northeastward from San Antonio to Austin, where it is about 300 feet high. It was observed by zoologist G. W. Marnoch and was described by Robert Thomas Hill in 1890. The escarpment, which appears from the plains as a range of wooded hills, separates the Edwards Plateau in the west from the Coastal Plains. The Balcones zone was formed under conditions of strain during the Tertiary era, when a downwarping occurred near the Gulf Coast with a moderate uplift inland. Water-bearing formations passing beneath the plateau to the plains are broken across by the Balcones fault group, and much water is forced to the surface by artesian pressure. Barton Springs, San Marcos Springs, and Comal Springs are examples of the resulting artesian wells or springs.