Interim geologic map of the Grouse Creek and Utah part of the Jackpot 30' x 60' quadrangles, Box Elder County, Utah, and Cassia County, Idaho (OFR-716dm)

By: Miller, D.M., Clark, D.L., Wells, M.L., Oviatt, C.G., Felger, T.J., and Todd, V.R.

This captivating map invites exploration of the dramatic landscapes spanning Box Elder County, Utah, and Cassia County, Idaho. It meticulously delineates the diverse geographic features of the region, from the rugged peaks of the Grouse Creek, Raft River, Goose Creek, Dove Creek, Matlin, Hogup, and Wildcat Mountains, to the expansive plains surrounding the iconic Great Salt Lake and the scenic Curlew and Rosette Valleys. This comprehensive map serves as an essential guide to understanding the very foundations of this geologically rich and historically significant corner of the American West.  

Delve into billions of years of Earth's history as this map unveils a remarkable array of geologic formations, each telling a profound story of planetary evolution. The most recent imprints of our planet's dynamic past are captured in extensive Quaternary surficial deposits, including alluvial, eolian, and mass-movement features. These reveal the influence of past climate, notably through lacustrine gravels and sands from ancient Lake Bonneville and the fluctuating Great Salt Lake, providing a rich record of hydrological cycles and past environments. Evidence of past glaciations is preserved as glacial till in the Raft River Mountains. Journey deeper in time to discover widespread Tertiary volcanic and basin-fill units, including voluminous basaltic and rhyolitic lava flows and the remarkably thick Salt Lake Formation (exceeding 10,000 feet or 3000 meters). The prevalence of these Cenozoic volcanic and sedimentary units strongly indicates the profound crustal stretching and thinning that characterized the Basin and Range extension in the western United States, with some rhyolitic tuffs even linking to the distant Yellowstone hotspot track. Most profoundly, this map highlights the ancient foundations: deeply metamorphosed Paleozoic and Neoproterozoic rocks, such as schists and quartzites, that bear the unmistakable marks of intense heat and pressure. The widespread occurrence of these highly deformed units across the Goose Creek, Raft River, and Dove Creek Mountains signifies major mountain-building events and crustal thickening during the Proterozoic Eon, laying the groundwork for subsequent geological evolution. Crucially, the map pinpoints the Archean Green Creek Complex, with rocks dating back an astonishing 2.574 to 2.650 billion years, definitively confirming that the oldest known rocks in Utah are found within the majestic Raft River Mountains and Grouse Creek Mountains. The exposure of these primordial rocks in the Raft River Mountains offers a rare window into the fundamental building blocks of the North American continent, providing invaluable insights into early Earth crustal formation and continental assembly.  

Designed at a scale of 1:62,500, this map is an invaluable tool for anyone fascinated by Earth's processes. While designated as an "interim" release, it represents the cutting edge of geological research, making the most current scientific data publicly available even before formal publication. This proactive dissemination of geological knowledge exemplifies scientific rigor and transparency, fostering collaboration and accelerating research. The map provides detailed insights into rock types, complex structural features like various fault types and fold axes, and the long-term evolution of the landscape. Whether for understanding regional geological frameworks, guiding mineral and water resource exploration, assessing environmental hazards like landslides, or serving as an exceptional educational and research tool, this map empowers users to trace the profound forces that have shaped this region. It bridges complex scientific research with practical utility, supporting informed decision-making and fostering a deeper appreciation for the Earth sciences among a broader audience. It is more than just a map; it is a portal to the past, revealing the enduring geological legacy of Utah and Idaho.

Published: 2020