This ant is native to South America but is widespread in California and a number of other U.S. states. It's a major pest in urban areas, and it competes with native ants in both urban and non-urban areas. Some Web sites with Argentine Ant information are here: (1)(2)(3)

My house is having an invasion of these ants right now, so I've had ample opportunity to photograph them running around on my kitchen counters.