The Hathaway Spur ran from a junction with the D&RG's Denver-Pueblo Main in downtown Castle Rock, CO (MP 32.61, Castle Rock Quarry Junction), out to the O'Brien Quarry, approximately 2.7 miles southeast. The route was constructed in 1882 as narrow gauge, converted to standard gauge in 1889, and fully abandoned sometime after 1923. The quarry stopped shipping product sometime around 1902.