These guys are very common within their range and it is extremely easy to see them in places like Sacramento in California's Central Valley. They build nests out of big balls of sticks that they place on power poles and you can see them in most suburban neighborhoods. Because of their relatively narrow range there was great concern that they might be wiped out by West Nile virus, and their numbers did drop down, but hopefully that has passed.
Here's a comprehensive webpage with many resources for the species: Yellow-billed Magpies
Saw one or two of these birds kicking around the centre of Sacramento when I was there. Kicking myself to this day I wasn't quick enough with my camera!