If you are OK with dark, cramped spaces, according to the World on Wheels blog, Gold Bug Park and mine are accessible! (Though, transportation to the site will need to be arranged by visitors)

https://wheelstraveler.blogspot.com/2021/06/accessible-attractions-californias-gold.html

wheelstraveler.blogspot.com

ACCESSIBLE ATTRACTIONS: California's Gold Country Region

Our ratings are... Fully Accessible - You can access all of the attraction, with no problem, in any type of wheelchair. Mostly Accessible - ...