To find this trail, head up Keystone Gulch Road about 0.2 miles until you see a large beaver pond on the right. Just past the pond, there's a road that goes through the creek. You can ford the creek or use the nice bridge 50 feet upstream.
Now turn back in the downstream direction and hop on the trail. Pay attention and you'll see a diverted water stream flow into a pipe, and then you'll be riding right on top of it. Continue on very level easy terrain until you need to go around a cliff. The trail is skinnier here, and there are some wooden planks on top of parts of the exposed pipe for about 50 feet. If you're a total beginner, feel free to walk this section!
Turn the corner to big views of the distant Gore Range and continue to roll along this scenic trail until you hit Keystone Ranch Road.