From the Utah Geology site, location #21, it says: "Directions to Site: This location is reached from the westbound lane of I-70 about 2.5 miles west of the interchange with Utah Hwy 24 to Hanksville.  The turnoff is a gravel road passing through a gate in the interstate fence, located between the "Rest Area, 1 Mile" sign and the rest area itself. As of this writing, blue ribbon on the highway reflector marks the turn. If you miss this turn it is many miles to an interchange.  Once through the gate take the fork to the right (rather than crossing the wash), turn right at the second intersection and drive about 0.3 mile to the bluff near the north side of the interstate.  Walk along the base of the bluffs and in areas below the outcrop horizon of the nodules.  They will be scattered abundantly on the ground."

The marker should be very close, the website had a marker but no coordinates so I tried to match the location on Google maps.