Drones?

Not sure, but I would point you in the direction of local Border Patrol or the 148th Fighter Wing (most likely the former). Odd stuff!

I suspect it was an unmanned drone aircraft.  As stephanos notes, they are used by border patrol.  Likely a training flight.

Or aerial imaging?

Dennis O'Hare has some sort of UAV, not sure if it is a plane or helicopter,  though. He uses it a lot for photos around the harbor.

If by "drone-like" you mean "piston-engine with a delta wing," I believe it was the Dyke Delta JD-2 belonging to Alan White of Superior.  I've seen it a coupe of times, and it was definitely flying over the Harvest Festival last Saturday.

Says there the 'Dyke' is a Momoplane.  Who named that dirty cock sucker anyway?  Sounds kinda intriguing.  That, and you can build one for 30-50k.  I'm in on the low end?  Could I swap out the engine in my lawn mower?