Here is the exact route from the intersection of I-70 and Hwy 77 at Junction City.
http://www.marengo-ltd.com/map2/index.php?route=738
(You can scroll in to see more detail such as the minor road names.)
Drive West to Milford Lake Rd.
Drive North until you run into the lake at 244.
Head West, the road will curve to the North.
Keep heading North following the curves all the way up until the road curves to the West.
Turn Right and head East on Luttman Rd. (This turns into gravel.)
You'll soon see the School Creek ORV sign.