On most days, there's usually only 2 to 3 KC-10s or KC-135s in the air at this time of night.
Of the 31 Trackable Military Aircraft over CONUS, 12 are air refueling birds. An E-8 Joint STARS shut it's transponder off a few minutes ago while flying westward.
4 of the refuelers seem to be headed to the same area off of San Fran (pic related), suggesting they are refueling a lot of aircraft for some reason.
You can verify: https://global.adsbexchange.com
Go to the map menu –→ Filters –→ Military