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.

Utah's landscape is among the most spectacular in the world. It is a region of prominent peaks, sweeping valleys, dramatic canyons, and plateaus rimmed by sheer cliffs. Unique among western states, Utah's landscape includes the Colorado Plateau, Basin and Range, and Rocky Mountains geologic provinces. Exposed rocks tell the geologic story of the region's basement structures, overlying surface features, and rock sequences that have contributed to sculpting the appearance of today's landscape. Rocks and formations record the evolution of the western part of the North American continent, and give clues to the nature of ancient crustal basement and Earth's deeper layers. Climate change has shaped the present landscape through the erosional power of ancient glaciers and the presence of today's large lakes and basins. Geology of Utah introduces the state's deep earth, plate tectonics, and the development of its ancient mountains. It describes the geology of the three main geological provinces, ancient elevations, cliffs, valleys, and the history of the region's climate. This book will enrich the experience of enthusiastic amateur geologists who want to understand and explore the development of Utah's highlands and the history of this dynamic landscape.