Chinese tallow, Triadica sebifera. Invasive species in Ca. https://www.cal-ipc.org/plants/profile/triadica-sebifera-plant-profile/

@floral_uk that is very useful thanks. That plant has deep tap roots rather than broad shallow roots. So I guess that would make it less suspicious as the tree that is undermining a patio 25 feet away?

I can only identify it for you and can’t offer any advice. I’ve never knowingly been anywhere near one irl. They don’t grow here afaik. But I do know it’s banned from sale in the EU

"That plant has deep tap roots rather than broad shallow roots. "

It is not an either/or proposition. It has both a taproot/anchorage root as well as a broadly spreading, shallow system of feeder roots........as do virtually all other tree species. In fact, one of the reasons beyond seeding freely that makes this species invasive is its ability to generate root sprouts at a significant distance from the mother tree.

So yes, it could definitely be affecting a patio 25' away.

@gardengal48 When I follow the path of roots through the yard, the facts appear to agree with you. The Chinese Tallow roots are like a sea serpent poking its body above the water in different places. The surface texture of those roots exactly matches the bark pattern on the Tallow.