National Forest Development Road 623 is a hiking, biking, and horse trail in White Pine County, Nevada. It is within Humboldt-Toiyabe National Forest. It is 7.9 miles long and begins at 7,114 feet altitude. Traveling the entire trail is 15.9 miles with a total elevation gain of 3,603 feet. The Great Valley Mine (elevation 8,104 feet) quarry can be seen along the trail.