This covers the extensive but fairly undeveloped bouldering along the Geology Tour Road. While a majority of the problems are close to the road some problems require hiking as much as 30 minutes or more. Good coverage exists in the Joshua Tree Bouldering Guide (Miramontes) but lots of new stuff has gone up since it's publication.
The unpaved, but occasionally graded, Geology Tour Road is a fairly good dirt road with lots of washboards and ruts in the first few miles and then a fair bit of soft sand after that. While having a 4WD vehicle is not a necessity it is advisable to have a vechicle with a bit of clearance and one that you feel comfortable driving over the odd rough spot. Be aware that some of the parking spots have a fair bit of soft sand which can spell trouble for those without 4WD, especially if trying to turn around in it. Better to keep the vehicle pointed downhill and drive the extra bit to Squaw Tank where a good turnaroud exists.
Below is a list of mileage for various spots along the road (mileages listed from the start of the Geology Tour Road).