Preliminary Digital Database for the Bedrock Geologic Map of the Lower Granite Gorge's Proterozoic Geology, Grand Canyon, Arizona

This Geologic Map Schema (GeMS) database contains all the geologic map information used to publish the 1:24,000-scale Geologic map of the Lower Granite Gorge of the Grand Canyon, Arizona. The data were prepared using ArcGIS Pro software by Esri and are formatted according to the GeMS standard. The geospatial database builds on an unpublished 1:24,000-scale bedrock geologic map of Lower Granite Gorge made/drawn by K.E. Karlstrom in 1994. New field and digital mapping were conducted from 2023 - 2025 on research river trips. The database is part of a USGS Scientific Investigations Map (SIM), which also includes two plates, showing the 1:24,000-scale map and cross section, and a pamphlet. This preliminary database will be superseded by an updated database that will accompany a USGS (SIM), which has been scientifically reviewed and is in the final editing stages prior to its publication. When that process concludes, the content of the database will be updated to reflect any changes to the map manuscript that occurred during final editing. The well-exposed basement transect in the Lower Granite Gorge (LGG) of western Grand Canyon provides a middle-crustal record of suturing crustal blocks during the Proterozoic accretionary history of southwestern Laurentia. Located at the center of the LGG, the Gneiss Canyon shear zone (GCsz) juxtaposes two major crustal provinces and records the cryptic suturing between the isotopically evolved Mojave crustal province to the northwest and the juvenile Mojave – Yavapai transition crustal province to the southeast. The GCsz marks an abrupt westward increase in metamorphic grade, decrease in the age of calc-alkaline plutonic complexes, increase in paleo-crustal thickness, and a shift to more evolved crustal isotopic signatures in Hf, Nd, O, and Pb systems. The LGG records three main deformational events during the Proterozoic: at ca. 1.75–1.72 Ga, at 1.71–1.68 Ga during the Yavapai orogeny, and during the 1.47–1.37 Picuris orogeny. Basement was unroofed to the surface by Cambrian time, then buried by ~1 kilometer of Paleozoic strata and ~2 kilometers of Mesozoic strata. Cenozoic uplift and deformation related to the Laramide orogeny produced north- to northeast-striking reverse faults and monoclines that were later reactivated as normal faults during Miocene and ongoing Basin and Range extension.