Certain campgrounds on the Pacific Coast have been raided by bike thieves at night that specifically go after the bikes in the hike and bike sites, along with anything else that's not nailed down--generators are another popular item. Half Moon Bay had a really bad rep for this in the past. Bikes in San Francisco will also vanish, even though locked.
If you have to leave it outside a place with wifi, make sure you can keep the bike in sight through the window. You may also invest in a motion alarm, or at least a fake one with blinking LED that may give a thief pause for reflection.