We called it winter rye when I lived in SoCal. Where are you located? It makes a difference as Big Bear Lake, Upland, and Malibu are all considered the LA area.

I live in La Puente, part of LA county. Based on images I found online it also looks a lot like something called "rescue" grass.

La Puente is good. LA, itself, is a fairly cool area of SoCal. La Puente gets much warmer, though. My wife grew up in El Monte and had a bermuda lawn that worked great. What kind of grass do you have? And if you tell me it is Marathon, I'm going to get a little pissy about it. You should have a warm season grass like bermuda or St Augustine. You are 10 miles too far inland to be trying to grow Marathon 1, 2, or 3. Marathon in the heat takes too much water for an area with perpetual drought issues. So having said all that, the way to get rid of the problem grass is different depending on which lawn type you have/want.

We have St Augustine (mostly) with a little Bermuda trying to make its way in. I used to just pull these weeds by hand but got lazy one year and now it spread a lot more, especially in a few bare spots.