The first section of this trail was part of the original Old Half Moon Bay to Colma Road (HMB-CR), which opened in 1879. San Pedro Mountain rises about 970 feet from sea level at Devil's Slide to this junction in less than half a mile. From there, the ridge has a broad top that rises only about 80 feet over the next half mile to the top of San Pedro Mountain. I love this section. It is sunny, covered with flowers, and has sweeping views in all directions. The trail follows the ridge, and then drops down to Old San Pedro Mountain Road
(OSPMR), which opened in 1915 as a replacement for the HMB-CR.
There is no easy way to make this trail part of a full loop. I generally run it in one of two ways. The first is to run up the HMB-CR, follow the full length of the San Pedro Mountain Trail (and possibly beyond), and then return the same way. The second way is to run up OSPMR to the junction with the rugged "Mile" trail, run up that, cross the San Pedro Mountain Trail to the OSPMR and then return via that road.
It would be great to be able to run up the HMB-CR, cross the San Pedro Mountain Trail, and then run down via OSPMR. However, currently, unless you have two cars, there is no easy way to get back to the starting point.
The HMB-CR and OSPMR each have a very large variety of chaparral flowers, grasses, and trees. They start blooming early and stay green longer than neighboring areas. San Pedro Mountain trail itself is sunny and somewhat drier, so there are fewer varieties. However, if you go the two ways that I mentioned above on two separate trips, you'll see just about every common variety of flower, tree, and plant that grows in the coastal region.