Arnold Number 1 Reservoir is a reservoir located in Niobrara County, Wyoming. It appears on the Wagonhound Creek NE USGS 7.5-minute topographic quadrangle. The elevation at this location is approximately 4,455.84 feet (1,358.14 m) above sea level. The nearest populated place is Underwood Crossing, approximately 8.6 miles to the NW.