The California Molecular Cloud
  We present an analysis of wide-field infrared extinction maps of a region in
Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis
we have identified a massive, nearby, but previously unrecognized, giant
molecular cloud (GMC). From comparison of foreground star counts with Galactic
models we derive a distance of 450 +/- 23 parsecs to the cloud. At this
distance the cloud extends over roughly 80 pc and has a mass of approximately
10^5 solar masses, rivaling the Orion (A) Molecular Cloud as the largest and
most massive GMC in the solar neighborhood. Although surprisingly similar in
mass and size to the more famous Orion Molecular Cloud (OMC) the newly
recognized cloud displays significantly less star formation activity with more
than an order of magnitude fewer young stellar objects than found in the OMC,
suggesting that both the level of star formation and perhaps the star formation
rate in this cloud are an order of magnitude or more lower than in the OMC.
Analysis of extinction maps of both clouds shows that the new cloud contains
only 10% the amount of high extinction (A_K > 1.0 mag) material as is found in
the OMC. This, in turn, suggests that the level of star formation activity and
perhaps the star formation rate in these two clouds may be directly
proportional to the total amount of high extinction material and presumably
high density gas within them and that there might be a density threshold for
star formation on the order of a few times 10^4 hydrogen molecules per cc.
