Were they actually deadheads (NRPS -- company paid travel to position a crew) or commuting (NRSA -- choosing to live/visit away from base and commute)?

I wouldn't be at all surprised at a bunch of commuters from somewhere as nice as SBA, but I'd be quite surprised at that many deadheads (meaning that United would have flown them in working on revenue flights but not had outbound revenue flights for any of them to work) absent an irrops situation.

(IIRC, if they're commuting it's their responsibility to get to the originating station for their first paid leg to check in on time and if not they're "charged" for the delay and they face nasty disciplinary action, on the other hand if they're deadheading it's the company's responsibility to get them to their next leg on time)