Yes, I have digging up my backyard because the soil is so bad I couldn't get anything to grow this year, I started noticing "rocks " that seemed out of place. I researched my address and the house was built in 1900. Everything I find is 2 to 3 feet deep.
Not out of place your in or close to the Delta and major rivers that have been moving all over for millions of years . And the foothills to the east have large alluvial fans that reached the valley floor cobble is everywhere . Do you have a leach field ? or on city sewer ?
The eggstone rock looks like gabbro which is interesting. The other piece looks like a quartzite cobble. It is reminiscent of a hoof pestle though. I'm curious of what some of the more experienced guys here think. I'm from California as well. Southfork would know better then me.
It's city sewer now..but when I researched address it was farm land in 1900. I also found that there had been an archeological site not far from me a few years back. I have several items I would love someone to look at