CR 175 climbs for 12 miles one-way from 7,000ft Salida to close to 10,000 feet, way up in the Arkansas Hills. Ridden as an out-and-back this would make for a 24 mile ride with a ton of climbing, gorgeous views, and plenty of options to keep riding and/or turn this into a big gravel loop. Some singletrack trails also connect to this road, offering up more interesting routes.
Park in the gravel lot near the bridge across from the hospital.
http://www.singletracks.com/item.php?c=1&i=7473