This question is, in part, inspired from the 1997 Hollywood movie [Volcano][1], where a fictional volcano erupted out of the La Brea Tar Pits in Los Angeles. 

The [San Andres Fault][2] is a transform fault plate boundary (see image below):

![enter image description here][3]

Image from the [USGS Glossary entry for transform faults][4], with a definition:

> A transform fault is a special variety of strike-slip fault that accommodates relative horizontal slip between other tectonic elements, such as oceanic crustal plates.

A specific type of transform fault is a 'leaky transform fault', which according to a source used on its [Wikipedia page][5] describes the tectonic movement at this type of faulting as being:

> In addition to the regular strike-slip motion observed at transform boundaries, an oblique extensional component is present, resulting in motion of the plates that is not parallel to the plate boundary.

Illustrated below:

![enter image description here][6]

**Is there any evidence that oblique tectonic movement occurs along the San Andreas Fault?**

**Hence, is a San Andreas volcano possible?**

  [1]: http://www.imdb.com/title/tt0120461/
  [2]: http://geology.com/articles/san-andreas-fault.shtml
  [3]: https://i.sstatic.net/w9odS.gif
  [4]: http://earthquake.usgs.gov/learn/glossary/?term=transform%20fault
  [5]: http://en.wikipedia.org/wiki/Leaky_transform_fault
  [6]: https://i.sstatic.net/Z3VGP.png