Follow the BLM signs...
Pretty much every turn is marked. There is a sign for Sand Wash / 9-Mile Canyon off US-40, it's the first real turn after the gas station. It's paved a long ways out now for the oil trucks, way more than 10 years ago. Every major turn is marked with a small wooden sign, if it's not marked stay on the more "major" looking road. You'll roll a little bit, then climb up high enough to see back to Split Mountain clearly, then start dropping into the canyon. I wouldn't even trust Google satellite views for turn-by-turn directions, one new set of gas wells and they'll open up a new road.
Also, be SUPER careful if the road's wet. The shale turns to grease in the rain.
Have a great trip!
EDIT: Just saw you're coming from PC. The turn off is still marked, you just have to actually pay attention as you get close to Myton not just wait til the gas station and then watch.