You will need a 4×4 for this, might not use 4×4 but your going to want the ground clearance.
From Ukiah or Eureka- Heading North or South on highway 101 get off on highway 20 towards upper lake. Stay on 20 till you past Mendocino lake and the next passing lane coming up get in the left lane. About half mile up there is a left turn lane onto potter valley Rd, turn there. Stay on Potter Valley Rd for about 10 minutes were you will automaticly be on main street of potter valley town. Turn right on Eel River Rd there will be a tiny gas station and bar where you turn, Now follow that road up the mountain and at the top of the mountain you can take the fork to the right or left, right is easiest. Now you will be merging right back onto Eel River Rd so watch for cars. Now this is were you have to pay attention, there will be a dirt road on the right side take it make sure its before the bridge. Now you will come to a gate were you can drive around or over keep going down that dirt road 3 miles and after you pass 2 left turn take the 3rd one down, it will be nice and open and there you will see both hippie rocks. Also be carefull rocks do shift around every year so check your jumping area. Make sure you take the right roads people around there do not like people on there property.