There is one in San Francisco, San Jose & Hayward (but I do not believe there is one in San Carlos). I wish there was.
SAN FRANCISCO GREYHND STA
425 MISSION TRANSBAY STA
FLR 3
San Francisco, CA 94105
(Note: I don't know why this says 3rd Fl. I have been to this location and it is on the ground floor (righ under an overpass).
SAN JOSE GREYHOUND STA
70 S ALMADEN AVE
San Jose, CA 95113
HAYWARD GREYHOUND STA
699 B ST
Hayward, CA 94541
Guy, I am going to be taking something over to the Hayward Depot either this week or early next week. If you need me to take something with me to drop off, let me know.