Grass Valley East Dike, also known as Harvey Gap East Dike, is a vital structure located in Garfield County, Colorado, near the city of New Castle. The dike serves the primary purpose of irrigation, harnessing water from the West Elk Creek-OS for agricultural use. Constructed in 1946, this Earth-type dam stands at a height of 12 feet and has a hydraulic height of 10 feet, with a length of 450 feet and a storage capacity of 2091 acre-feet.

With a significant hazard potential and fair condition assessment, Grass Valley East Dike is regulated by the Colorado Department of Water Resources (DWR) and undergoes regular inspections to ensure its structural integrity. The dam's spillway, with a width of 15 feet, is uncontrolled, and the maximum discharge capacity is 462 cubic feet per second. Despite its moderate risk rating, the dike has been deemed to meet safety guidelines, although further risk management measures may be necessary in the future to mitigate potential hazards.

As a crucial component of the local water resource infrastructure, Grass Valley East Dike plays a crucial role in supporting agricultural activities in the region. With its stone core and rock foundations, this dam represents a key element in water management for the area, providing essential irrigation resources for farmers and contributing to the overall sustainability of the ecosystem.