This is a pretty good trail system when kept up. The time I rode it, it was kind of creepy because I came up a hill and there was some redneck dude with a gun sitting on a tree waiting to blast bambi. Make sure you don't ride alone! It had some great climbs and downhills but also some overgrown parts, if you ride in the late fall it's a lot better than summer. They did have a race there this past summe, so I'm assuming it's been kept up better than the last time I rode the trails. Worth the drive out.
Take Hwy 218 south from Iowa City, turn right heading east onto Hwy 92 to Washington, IA, head south (turn left) on hwy W55, turn left onto Sockum Ridge Rd, the park is on your left.
http://www.singletracks.com/item.php?c=1&i=1459