Located in La Plata, Colorado, Pastorius - Main Dam is a private earth dam completed in 1903 primarily used for irrigation purposes along the West Fork Cottonwood Gulch-OS river. With a height of 26 feet and a length of 1090 feet, the dam has a storage capacity of 565 acre-feet and a surface area of 45 acres. Its spillway type is controlled with a width of 53 feet, and it is equipped with one slide (sluice gate) and two valve outlet gates.

Despite being in fair condition as of the last inspection in August 2020, Pastorius - Main Dam holds a significant hazard potential and is classified as having a very high risk level. The dam is regulated by the Colorado Department of Water Resources and undergoes regular state inspections and enforcement measures. While it serves multiple purposes including fish and wildlife pond creation and recreation, its primary function remains irrigation for the surrounding area. With its historical significance dating back over a century, Pastorius - Main Dam stands as a vital water resource structure in the region for both agricultural and environmental needs.