I went to an internet yellow pages search, typed in your zip code and requested search by business category. There’s one listed, but no clue if it’s 24 hour.
Try searching for “self-service laundry” instead of laundromat. Laundromat used to be a registered servicemark, so it wasn’t used as a general term in telephone directories.
Surely, one of these has to be open overnight? That list has the 272 self-service laundries within 45 miles, starting with the closest and circling outward. I’m sure one of them has to be open all the time.
Google Local is excellent for this sort of thing, BTW.
Funny you should ask. I used to live in San Jose and wanted the exact same thing. Never did find one very close, but I did eventually find two:
Mountain View, corner of Shoreline Road and Montecito Ave. In the Safeway plaza (around on the side, not visible from the street).
Watsonville. I also happened to like to go for long drives on windy roads in the middle of the night, so I’d go Almaden Expressway -> McKean Rd -> Uvas Rd -> Watsonville Rd -> Hwy 152 -> Hwy 1 -> Hwy 17 -> Hwy 85 -> Almaden Expressway. There’s an all night laundromat on 152 just when you come out of the mountains into Watsonville, along the straight stretch of road that’s still not quite in the dense part of town. On the left, probably right around here. Called Mother’s or Grandma’s or something like that, not that it’s necessarily still called the same thing. Nice drive, even if you don’t stop and do laundry.