In case you didn't know, there has been a sizable earthquake swarm in Long Valley. The last update I saw stated the current swarm had produced over 600 quakes. While most of these quakes have been small, a number of them have been in excess of magnitude 3.0. The USGS states that the quakes are currently tectonic in nature and that there is no sign of magma movement. You can find data on the quakes at the link below.
http://volcanoes.usgs.gov/volcanoes/long_valley/long_valley_monitoring_1.html
Take a look at the data. The top down view shows a coverage of about 4km from east to west and 6km from north to south. The image that shows the depth and magnitude shows quakes at about 4km below the surface and extending to 8km. So the range from top to bottom is approximately 4km. The magnitude of the quakes weaken as you go from the bottom to the top. The interesting part is how the stronger quakes line up with the top part of molten magma, the weaker quakes with the congealed magma, and the weakest quakes with the "basement."
I am attaching some images so we can preserve the data.
Long Valley top down view of quakes
Source: USGS
Long Valley side view
Source: USGS
And now for the interesting image that shows the setup of the caldera.
Long Vally cross section
Source: http://commons.wikimedia.org/wiki/File:Long_Valley_Caldera_cross_section.svg
by 
I have a selfish question. How will this affect Calaveras county CA? Say long valley blew, would that county of calaveras be on the map still and is it downwind from ash, or out of danger?