Calkins, also known as Hetzell, is a private dam located in Boulder County, Colorado, specifically in the city of Platteville. Constructed in 1879, this earth dam stands at 8 feet tall and spans 705 feet in length, providing irrigation for the surrounding area. The dam has a storage capacity of 187 acre-feet, with a normal storage level of 90 acre-feet, covering a surface area of 17 acres.

Despite its age, Calkins dam is classified as having a low hazard potential, but with a high risk assessment rating of 2. The last inspection of the dam took place in September 1985, with an inspection frequency of every 6 years. While the condition assessment is currently not rated, the dam is state regulated and subject to inspection, permitting, and enforcement by the Colorado Division of Water Resources (DWR). With its location on St. Vrain Creek, Calkins dam plays a crucial role in the irrigation system of the area and continues to be a significant water resource structure in the region.