they're basalt columns. they're not custom made by any means. it's the way it formed when coming up from volcano's years ago and it forms into those shapes. Look up "basalt columns" or "basalt rocks"

They're quite common in the Pacific Northwest and surprisingly affordable.

they also make for GREAT retaining walls, but heavy as _______

Thanks so much! Do you (or anyone) have any recommendation on where to get these type of stones in Bay Area California?

i really don't know about in the bay Area, but i do know in the Tri-Cities of washington there are a few stone guys that sell them affordably. I'm up in Spokane, they're quite popular here as well.

best of luck on the search... this might be where google becomes your best friend!

In Northern Ireland they come from the Giant's Causeway!