CALAVERAS PLUG

Along the old haul road, we see present day erosion cutting down through unconformities resulting from the past erosion and the following deposition. These rocks are from the Torrey formation.
An old erosional surface can be seen as a wavy line of pebbles on the face of the road cut. Again the main body is part of the Torrey formation.
A closer view of this road cut shows a younger stream filled channel cutting through the pebble lined unconformity.
A much closer view of an old stream filled channel with its course sediments stands out from the old sandstone stream bed.
Evidence of past faulting in the San Dieguito area shows a graben centered between two horsts.
A closer view shows the foot wall and the hanging wall of a normal fault. The rock is part of the Torrey formation with the typical cross bedding seen.
More faults in the sandstone rock of the Torrey formation are seen east of Encinitas. Following the pebble line the typical basin and range topography of the Eastern Sierras is seen in miniature.
A close up shows the nearly vertical fault line with the resulting offset of rock to the right and left.
The green sandstone and mud stone of the Del Mar Formation is seen along the Green Valley on the way to the Calaveras Plug area.
At the Calaveras Plug, the resistant conduit of an extinct volcano shows good columnar jointing and the resulting columns.
A cross section of one of the broken columns found on the talus pile at the base of the plug shows the characteristic six-sided columnar joint pattern
Devils Tower in Wyoming and
Devils Post Pile near Mammoth mountain in California are two classical examples of volcanic structures showing columnar jointing.
Looking from the columns towards the right a light red colored contact zone can be seen separating the conduit and the surrounding country rock
A closer view shows the dacite igneous rock of the plug, the metamorphosed rock of the contact zone, and the surrounding country rock.
An exploratory mine shaft dug into the hillside at the Calaveras Plug area. In volcanoes of this type many economic minerals are sometimes found.
A good view of the interesting patterns found in the rock seen inside the exploratory mine shaft
Closer view of the rock.  Some believe that this is the result of the weathering of the dacitic rock of the plug,
At one time few miles east of Rancho Santa Fe, a mineral called pyrophyllite was mined.  Southern California Volcanic Mountains can be seen in the background.
A close up of  evidence of past mining for  pyrophyllite (used in the production of insecticides) is shown here (homes now occupy this area to the east of  the SDG&E right of way.)
The characteristic color and plate like structure of pyrophyllite can be noted in lower portion of this picture. It's texture is reminicent of the colored rock at Calaveras plug.