Leave Collobrieres on the D14 and at the fork in the road take the left hand being the D41. continue on this road for 20k, then turn right onto the N98 and follow for about 5k. Turn right onto the D559 which will bring you into the small coastal town of Le Lavandou. Total distance for this section is only 26k (end of part 2).
Montezuma Valley road is loaded with tight, decreasing radius and mid to low speed corners. The view is spectacular from a height of over 3000 ft to the desert floor below but be sure to keep your eyes on the road as the drop off's are VERY steep. This is a favorite SoCal sport bike road so there will be some fast company on the way down and back up. The road was just repaved and is perfect - just watch for rock fall from the cliffs putting debris on the inside radius. There are some great places to eat and stay in Borrego Springs and it will set you up to ride back toward San Diego over some great mountain and desert roads.