Identifying a rock found on a Northern California beach

[Krista71]

I need help in figuring out what type of rock this is. I found it on a beach along the coast of Northern California.

 

[Rive]

Honestly, looks like concrete (after some rounds of rolling around).

 

[Baluncore]

Welcome to PF.
Maybe man made concrete from early construction industry.
Pudding stone or conglomerate if the included pebbles are rounded.
Polymict conglomerate if the pebbles are different.
Breccia, if the larger fragments are jagged.