Find the main shutoff. In a lot of San Diego slab houses it is on an exterior wall, in the garage, or in a box at the front of the house near the meter. Turn it clockwise until it stops. If you cannot move it, close the angle stop at the fixture that is spraying, and if water is near outlets or a ceiling light, turn that breaker off.
Do not stand in water and flip a breaker at the same time if you can avoid it. If the ceiling is sagging, get out from under it. A soaked drywall lid can come down.
Then call. This line plays a greeting and takes a message. Leave the address, the city, and whether you got the water stopped. A plumber still has to see the break. An emergency visit typically runs $175-$650 before parts, and more if the repair needs material the same day.
A burst at a fitting can sometimes be a local repair. A burst in galvanized or a second leak in the same month is a reason to talk about a repipe, not to pretend the patch is the whole story. We connect the call. The plumber does the work.