From I-70, take Exit 176 for Vail. Take your first right thru the roundabout on to North Frontage Road (you will now be traveling on the north side of the interstate and driving west.) At Red Sandstone Road turn right, and follow the paved road about 0.7 miles, past two switchbacks. Just before the sharp curve to the right (3rd switchback) the dirt road you need to take will be a left turn on the curve here. There should be a large green Forest Service sign indicating this is Red Sandstone Road #700 (Reset your odometer here). As you head generally north on this road, it will have frequent sharp curves and changes in direction as it crosses several drainages.
Continue for about 2.7 miles to a fork in the road at Lost Lake Road (#786). Keep left here to stay on Red Sandstone Road.
Around mile 6.5 you will pass Red and White Mtn Road/FSR 734 which forks to the left - Stay straight. At mile 6.7 you will pass another fork to the left for Muddy Pass/Moniger Road. Stay straight. Immediately after, the road begins to drop on two switchbacks down a forested side of the mountain to the Piney River.
When you are just over two miles from the ranch, you will cross a small bridge over Piney River. Follow the road as it curves to the right, where you will see a sign for Piney Lake two miles ahead.
You will reach a Forest Service parking lot on the right at mile 10.65 before the entrance to Piney River Ranch. If you are only hiking, and not a ranch guest, park in this lot. The trailhead is on the north side of the parking lot (left side of the parking lot as one faces the Piney River Ranch entrance). Allow up to 45 minutes to make this drive.
At the crossing of Piney River and along the two mile stretch of road after that crossing that leads up to the ranch, there are numerous primitive site opportunities. However, we offer the following warning. On one of our two visits here on a Friday evening, we found most every possible site taken and there were boisterous campers who kept us up much of the night with loud music, partying and even shooting off pistols in the middle of the night. On our second visit and overnight camp (which was on a Thursday evening this time) we were awakened at 1:00 AM in the morning by two very drunk men attempting to paddle a canoe down the Piney River in the dark. For 20 minutes or longer, we listened to their loud voices as they would get out of the canoe to get around some obstacle, splash around in the water, stumble, and then get back in the canoe. Eventually they were out of earshot, but our impression of this place is that it's the "in" spot for partiers.
If you want some peace and quiet, you may want to search for a primitive site somewhere along the Red Sandstone Road before coming to the Piney River crossing. There are some spots visible on Google Earth and on the two FS roads mentioned above that turn off to the left just before the descent down the mountainside to cross Piney River. Just be careful to not end up on private property.