Is this a massive snail fossil, nautiloid fossil, methane seep, or something else entirely?

[Beeradley]

While hiking along a dry creek bed I noticed an unusual protuberance of off white stone. I cleared some top soil away to discover a stone distinctly snail-like, clearly natural, and very large (3’ across). Comparing it to googled images leads me less toward methane seep and more towards some sort of fossilized organism. 
can anyone help me to understand and identify what I’ve found? Thank you, sincerely.

 

 

[Beeradley]

Also, here is location information-

Santa Cruz Mountains, California 

 

time/date: 10/01/2024

[DPS Ammonite]

There are no cephalopod or snail fossils that big in the Santa Cruz Mountains. It is a concretion.

[rocket]

I agree with @DPS Ammonite: no cephalopod or snail, a concretion

perhaps a fossil is inside, no one knows...