This website tells more about the mining history of the trail:
http://www.ncgold.com/Recreation/IndepTrl.html

The Independance Trail runs along an old mining channel on the side of a mountain high above the Yuba river. Miners used the channel to bring water to their claim areas and the trail itself is in the old channel. This makes the trail unique because although it's in mountainous terrain, there is almost no elevation gain and the trail is wheelchair accesible for most of it's length due to the flat, wide channel bottom. There is a nice 4 ft high berm between hikers and the edge so you can relax when hiking with children. This trail really makes mountain terrain accessible to people who would otherwise not get to enjoy it, but the views, bridges and historical remnants make it exciting for any hiker. There is even a fiddle tune that has been written for the trail!
The trail extends several miles in either direction from the trailhead, and it's possible to make a loop if you head west and then loop back along a swimming trail. Be careful if you venture down to the Yuba. This river is extremely treacherous for swimmers although it may not look like it!

TO TRAILHEAD: Take Hwy. 49 and go 5.5 miles north of Nevada City.