Here is a acover from the California Midwinter International Exposition, postmarked San Francisco, CA Jan 6, 1894 (5pm)to OAkland (received same day Jan 6-postmark on rear at 7:30 pm). The fair didn't officially open until Jan 27th, so can only assume this was
some prefair business.... still....

.
Don't see a lot of these floating around.
There as a thread a while ago on Expo covers, but didn't have this to show at that time. Enjoy.