Disclaimer: The route we took (and hence the path the GPX follows, heads down to the reservoir and out onto the 3rd Ring Road from there, however the security guard at the gate to the reservoir was very close to not letting us come out. Only go down to the reservoir if you are potentially prepared to hike back out the way you came, with enough food and water.
The trail starts here on 西三环 (left). Take the dirt path directly west (right).
Head through the gate (you may need to register if it is the fire season, but they should let you in). The path then heads up into the hills among these cut-out cliffs (right).
After about 2 km, the path crosses a road and you can head up these steps toward a temple. Before this point, you can deviate from the track to explore some of the summits nearby.
Head North around the temple and follow the path towards the expressway and this attractive rocky outcropping with a nice view.
After the rocky outcropping, take a right before the expressway and follow these paths North through some farmland. You can also go under the expressway through a village, but we opted to stay on the dirt.
Eventually you will need to head down this spillway of sorts (?) and come across a junction underneath a large expressway bridge. Take a right and head east down towards the reservoir. Follow the path around the reservoir (pictures on the right) and go through the gate back down towards 西三环.
If they don't let you through the gate, you will most likely have to backtrack to the trailhead, so don't go down to the reservoir unless you're prepared to hike back up!
Getting to the Trail Head
This trail is quite convenient to access. It starts about 10 meters off of the third ring road (西三环), near where it intersects with Haitun Rd. (海屯路), just south of Ziweicun (自卫村).
Baidu Maps: https://j.map.baidu.com/c5/25k
Google Maps: https://goo.gl/maps/PyMARZNjrtdPo8xE6
GPS Coordinates: 25° 5'27.35"N; 102°38'26.50"E (25.0909306, 102.640694)
Bus Stop: 海源北路西口 Haiyuan North (about a km south from the trailhead). Bus Routes: 70路; 83路; 85路; k13路; z82路