Precipitable water (PW) determined from GPS signal travel-time delays has proven to be a useful tool in regions where soundings are sparse in space or time. In California and Nevada, GPS is particularly useful because of the high density of GPS sites used for monitoring the motion of tectonic plates. Here we have constructed high resolution images of precipitable water over the region by interpolating precipitable water values obtained from hundreds of GPS sites using station pressures interpolated from North American Regional Reanalysis (NARR) values. We have chosen to look at the monsoon initially because it provides perhaps the strongest PW signal. When the PW images are animated and the summer season (JJA) is examined they clearly show the increase in moisture associated with the southwestern monsoon. Early in the time period the PW over the region is quite low, with PW values under 25 millimeters; as the monsoon regime takes over, PW increases to 40 mm or greater in the southern portions of California. A modification of the PW signal associated with the terrain can clearly be seen. In addition to the synoptic time-scale signal, there also appear to be detectable fluctuations associated with diurnal variation. Higher PW values are found to be associated with a variety of synoptic effects, including mountain and desert thunderstorms and higher nighttime temperatures. It is found that there is strong year-to-year variability in the strength of the monsoon in California. To further understand the typical monsoon and evaluate its variability in a changing climate, we have created a mean climatic state over the period of study that can be used in future studies of climate change in the region.