MONTANA'S 1:100K SEAMLESS GEODATABASE: PROGRESS, METHODS, AND DERIVATIVES

In December 2015, the Montana Bureau of Mines and Geology (MBMG) released its 1:100,000-scale NCGMP09-based geodatabase, which seamlessly combines 79 existing (legacy) 1:100,000-scale geologic maps. The geodatabase covers approximately 80 percent of Montana and will eventually include the entire state as additional 1:100,000 geologic maps are completed. The MBMG began this project in 2012 in response to requests for a statewide, seamless digital geologic map. This geodatabase has subsequently been used to create a number of derivative map products for use by the geoscience community.

The seamless geodatabase was created by migrating ArcInfo coverages of existing geologic maps into the NCGMP09 template. Major challenges included edgematching across map boundaries and distilling a consistent set of unit codes for the 839 geologic formations depicted in the 79 existing maps. As new 1:100,000-scale geologic maps are completed, they are added to the seamless geodatabase. Prior to publication, these new maps are edge matched with the seamless database, and the database is in turn updated where needed. Legacy 1:100,000-scale maps are typically not updated. The most current version of the seamless geodatabase is therefore considered the most up to date and definitive map product at the 1:100,000 scale.

The availability of a seamless statewide geologic map has allowed the MBMG to create a number of derivative map products, including maps showing volcanic fields, faults, and sedimentary units. The most recent derivative map product is a new database of Quaternary faults. Quaternary faults were identified and exported from the seamless geodatabase into a new geodatabase with additional fault attributes. This new Montana Quaternary faults database includes 608 faults, as compared to 119 faults in the legacy USGS Quaternary faults database. The Montana Quaternary faults database will be used to prioritize investigations of Quaternary faulting, and estimate geologic hazards in Montana. In addition, the MBMG plans to use the seamless geodatabase to develop a statewide landslide database.