Six Mile - Northwest, also known as Beasley, is a privately owned dam located in Boulder, Colorado, with a primary purpose of irrigation. Completed in 1892, this earth dam stands at a height of 14 feet and has a storage capacity of 2186 acre-feet. It serves the local area by providing water for irrigation and recreation, with a surface area of 124 acres and a drainage area of 3 square miles.

Managed by the Colorado Department of Water Resources, Six Mile - Northwest has a low hazard potential and is considered to be in satisfactory condition. With regular inspections and a moderate risk assessment rating, the dam is equipped with an uncontrolled spillway and has a maximum discharge capacity of 11,552 cubic feet per second. While it has not been significantly modified in recent years, the dam continues to play a vital role in the water resource management of the region, ensuring water availability for agricultural and recreational purposes in the area.