Urban Futsal LA: https://urbanfutsal.la/
Fridays and Sundays at 7 - Fridays are higher level, Sundays better for youngers. The last Friday of every month is "baller night" starting at 5 and the level is usually higher.
619 Futsal in San Diego. 619futsal.com
Play at Miramar College/Black Mountain Road, Canyon Crest High School, and also in San Marcos.
Soccer Kids America in San Diego, soccerkidsamerica.org
Play in Balboa Park, Spring Valley rec center and Colina Del Sol rec center.
Both are weekend (Sat or Sun) futsal leagues. You can register as an individual and they will place you on a team, or you can register as a team. I think the level of skill/competition varies and is a little random. Some seasons my kid has had pretty high level competition, other seasons not so much.
I would love to know about drop in futsal in San Diego if it exists!
The San Diego Water Tower league was indoor/arena soccer, not futsal. Played off the wall. Not as food for skill development IMO. And yes, it is closed for structural issues. I heard of a lot of kids getting injuries playing there. I think it was very old turf, kids crashed into the walls, etc.