The wars are hosted outside of the city of Los Angeles because as you go farther out, there's more space that is less occupied. Parks in the city are busy all the time and school grounds are usually locked on weekends to prevent property damage. I had to convince my dad to drive me to my first war when I was 13 out here and it was kind of a schlep. From Santa Monica on a Saturday morning it takes about forty minutes to get to the place where this war is being hosted.
Wars are generally hosted in the LA-area every two months or so, with the biggest one in June/July (sometimes, people travel out west for the December one, too). They're usually posted here, but if not, there's a Facebook group called SCUN (Southern California United Nerf or something, I don't remember the expansion) that will have the information you want. There are other groups but this is the main one.
If you wanted to start your own, all you would have to do is find a place where people won't get mad at you for being and invite a few friends to play with Nerf blasters. That's the easiest way to get anything going.
Thanks, man! I found out about SCUN just after I posted this, but I couldn't find their group, just the page (which has been inactive for a little over a year). I asked the moderators over there if they were still a thing, and they said that I should find the group on Facebook to get updates. I wan't able to find the group just then, but I will keep looking. Thanks again.
I have been looking to play at a war for some time now, and I simply cannot find any wars near me. All of the major nerf associations near me seem to be defunct, and I do not have any idea how to start my own association (nor do I have the time, as high school is a TON of work). Help a brother out, will you?