Vermilion Parish, Louisiana in the context of Vermilion Bay (Louisiana)

A geological map or geologic map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features. Geological mapping is an interpretive process involving multiple types of information, from analytical data to personal observation, all synthesized and recorded by the geologist. Geologic observations have traditionally been recorded on paper, whether on standardized note cards, in a notebook, or on a map.

Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed.

Erath /ˈiːræθ/ is a town in Vermilion Parish, Louisiana, United States. The population was 2,114 at the 2010 census, and 2,030 at the 2020 population estimates program. It is part of the Abbeville micropolitan statistical area and the Lafayette metropolitan area.

The Vermilion River, or the Bayou Vermilion (French: Rivière Vermillon), is a 70.0-mile-long (112.7 km) bayou in southern Louisiana in the United States. It is formed on the common boundary of Lafayette and St. Martin Parishes by a confluence of small bayous flowing from St. Landry Parish, and flows generally southward through Lafayette and Vermilion Parishes, past the cities of Lafayette and Abbeville. At the port of Intracoastal City, the Gulf Intracoastal Waterway crosses the river before the latter flows into Vermilion Bay, an inlet of the Gulf of Mexico. The river originates at Bayou Fusilier, which is fed by Bayou Teche; winds its way through Lafayette Parish; and drains into the Vermilion Bay below Vermilion Parish.

The river is a "consequent stream" or a "tidal river," which means that the Vermilion was formed from the bottom up. The river was created by Vermilion Bay: tides and other natural actions in the bay slowly eroded the marshes and other features of the landscape as the river crept northward. The process brought the channel that would one day become the Vermilion River as far north as Lafayette, Louisiana. Much later, a distributary of Bayou Teche made its way south and eventually linked up with the consequent stream, forming a true north-south flowing river.