The name comes from the bootleggers who once made use of the area, getting lost among the numerous hollows. It was also near the site of an ammunition works and uranium processing plant which necessitated the cleanup that lies under the large mound on Hwy. 94. Now, the trail is a 10.5 mile loop with a mixture of double and singletrack punctuated with old homesteads, rock formations, natural springs, and a waterfall crossing. This is a very scenic and enjoyable mountain bike experience.
The gravel/doubletrack sections are fairly flat. The singletrack sections are super-flowy with punchy rock obstacles that will reward you with great views and better riding, the trail can get technical in spots and is now a much longer ride due to the increased singletrack. Be advised that this 10.5 mi loop will take some riders 2 hours to navigate due to the amount of singletrack and the difficulty of the rocky sections. There is a central fire road that cuts the loop almost in half which can be used to shorten or lengthen your ride.
Trail surface varies from dirt to rock throughout the trail, and drains very well, except in the flats of the lower creek bottom.
The trail is open until 10 pm, so it's a good place to ride at night.
From the Highway 40/94 interchange: Take Highway 94 South approximately 5 miles. The trailhead parking lot will be on your right hand side. It is not very well identified as "Lost Valley". A good landmark is the shooting range at the top of a hill on the right hand side of Hwy 94. When you descend that hill the parking lot will be on your right hand side, at the very bottom. It can also be accessed by going 7.2 miles east on the Katy Trail from Klondike Park.