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We study the relationship between molecular gas and dust in the CaliforniaMolecular Cloud over an unprecedented dynamic range of cloud depth (Av = 3 - 60magnitudes). We compare deep Herschel-based measurements of dust extinctionwith observations of the 12CO, 13CO, and C18O J=2-1 lines on sub-parsec scalesacross the cloud. We directly measure the ratio of CO integrated intensity todust extinction to derive the CO X-factor at over 1e5 independent locations inthe cloud. Confirming an earlier study, we find that no single 12CO X-factorcan characterize the molecular gas in the cold ( Tdust<20K) regions of thecloud that account for most of its mass. We are able to derive a single-valuedX-factor for all three CO isotopologues in the warm ( Tdust>25 K ) materialthat is spatially coincident with an HII region surrounding the star LKHa101.We derive LTE CO column densities for 13CO and C18O since we find both linesare relatively optically thin. In the warm cloud material CO is completely inthe gas phase and we are able to recover the total 13CO and C18O abundances.Using CO abundances and deep Herschel observations, we measure lower bounds tothe freeze-out of CO onto dust across the whole cloud finding some regionshaving CO depleted by a factor of >20. We construct the first maps of depletionthat span the extent of a giant molecular cloud. Using these maps we identify75 depletion-defined cores and discuss their physical nature.

Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust