This bulletin serves not only to introduce the non-geologist to the rich geology of Millard County, but also to provide professional geologists with technical information on the stratigraphy, paleontology, and structural geology of the county. Millard County is unique among Utah’s counties in that it contains an exceptionally complete billion-year geologic record. This happened because until about 200 million years ago the area of present-day Millard County lay near sea level and was awash in shallow marine waters on a continental shelf upon which a stack of fossil-bearing strata more than 6 miles (10 km) thick slowly accumulated. This bulletin summarizes what is known about these strata, as well as younger rocks and surficial deposits in the county, and provides references to scientific papers that describe them in greater detail. Mountains North 30 x 60 (1:100,000-scale) quadrangles. These companion maps and this bulletin portray the geology of Millard County more completely and accurately than any previously published work.

This project compiles basic information on the most important geologic and infrastructural factors that would be considered when planning a new high-calcium limestone quarry such as: (1) data on existing pits and prospects, (2) chemical analyses of high-calcium limestone, (3) the extent and spatial distribution of geologic formations having good potential for high-calcium limestone production, (4) references for geologic maps covering existing pits and prospects, and analytical data points, (5) locations of transportation corridors, and (6) locations of cement and lime plants, electric power plants, coal mines, and metal smelters that are large consumers of high-calcium limestone.