Fast and fun. Not overly technical, not easy.
From the North side of Sioux City take Stone Park Blvd West. It will eventually become Memorial Drive. There is a fork in the road - stay left. Park in the lot just South of the East entrance. There is a trail head right there or go down the gravel 1/4 mile to another.
http://www.singletracks.com/item.php?c=1&i=1832