Rock outcrop area and number of sedimentary formations have been widely used as sampling proxies in paleodiversity studies and have often been found to correlate with apparent paleodiversity. However, rock exposure area is a better proxy for the amount of sedimentary rock available for study than the widely used measures of outcrop area (i.e., map area) or number of formations. With the use of remote sensing and a geographic information system (GIS), it is possible to quantify rock exposure area accurately on a regional scale. Rock exposure area does not correlate well with either outcrop area or number of sedimentary formations, and the proportion of rock exposed in different areas can vary considerably with proximity to the coast, bedrock age, lithology, land use, and elevation. Therefore, this suggests that the correlation of paleodiversity and rock volume estimates is best explained by a common-cause hypothesis, rather than a geologic sampling bias hypothesis. GIS methods offer an efficient and accurate method of quantifying regional sedimentary rock exposure and may provide a helpful approach to assessing rock record bias on patterns in the fossil record.

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