The hydrologic effects of proposed irrigation with groundwater of 8,320 acres of land in Muleshoe Flat, a 34 sq mi area in west-central Platte County, Wyoming, were assessed. Results generated by a digital groundwater flow model indicate that, at the end of a 40-yr period, groundwater level declines of more than 50 ft can be expected in an area of 12.5 sq mi and of more than 200 ft in an area of 7 sq mi. In addition, streamflow depletions of 4,300 acre-ft/yr can be expected in the Laramie River and 4,700 acre-ft/yr in Sybille Creek. Additional hydrologic field data collection prior to initiation of the proposed irrigation development would improve these assessments. Applications for the proposed irrigation wells were denied subsequent to the data collection and analysis described in this report. (Author 's abstract)