The project leads for the collection of most of this data were Heiko Wittmer, Christopher Wilmers, Bogdan Cristescu, Pete Figura, David Casady, and Julie Garcia. Mule deer (82 adult females) from the Siskiyou herd were captured and equipped with GPS collars (Survey Globalstar, Vectronic Aerospace, Germany; Vertex Plus Iridium, Vectronic Aerospace, Germany), transmitting data from 2015-2020. The Siskiyou herd migrates from winter ranges primarily north and east of Mount Shasta (i.e., Shasta Valley, Red Rock Valley, Sheep Camp Butte, Sardine Flat, Long Prairie, and Little Hot Spring Valley) to sprawling summer ranges scattered between Mount Shasta in the west and the Burnt Lava Flow Geological Area to the east. A small percentage of the herd were residents. GPS locations were fixed between 1-2 hour intervals in the dataset. To improve the quality of the data set as per Bjørneraas et al. (2010), the GPS data were filtered prior to analysis to remove locations which were: i) further from either the previous point or subsequent point than an individual deer is able to travel in the elapsed time, ii) forming spikes in the movement trajectory based on outgoing and incoming speeds and turning angles sharper than a predefined threshold , or iii) fixed in 2D space and visually assessed as a bad fix by the analyst. The methodology used for this migration analysis allowed for the mapping of winter ranges and the identification and prioritization of migration corridors. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 67 migrating deer, including 167 migration sequences, location, date, time, and average location error as inputs in Migration Mapper. The average migration time and average migration distance for deer was 12.09 days and 41.33 km, respectively. Corridors and stopovers were prioritized based on the number of animals moving through a particular area. BBMMs were produced at a spatial resolution of 50 m using a sequential fix interval of less than 27 hours. Due to often produced BBMM variance rates greater than 8000, separate models using BBMMs and fixed motion variances of 1000 were produced per migration sequence and visually compared for the entire dataset, with best models being combined prior to population-level analyses (62 percent of sequences selected with BMMM). Winter range analyses were based on data from 66 individual deer and 111 wintering sequences using a fixed motion variance of 1000. Winter range designations for this herd may expand with a larger sample, filling in some of the gaps between winter range polygons in the map. Large water bodies were clipped from the final outputs.Corridors are visualized based on deer use per cell, with greater than or equal to 1 deer, greater than or equal to 4 deer (10 percent of the sample), and greater than or equal to 7 deer (20 percent of the sample) representing migration corridors, medium use corridors, and high use corridors, respectively. Stopovers were calculated as the top 10 percent of the population level utilization distribution during migrations and can be interpreted as high use areas. Stopover polygon areas less than 20,000 m2 were removed, but remaining small stopovers may be interpreted as short-term resting sites, likely based on a small concentration of points from an individual animal. Winter range is visualized as the 50th percentile contour of the winter range utilization distribution.