I grew up in El Portal (c. 1948- 1958) . My best friend lived in Sherwood Forest and the mound was directly across from her house.
The "cave" entrance was across the street and may have been on the property of the owners there. It went under the road and was not visible from the mound itself. I saw it, but never went in. It was being used for storage, mostly wood, I believe.
I often wondered if it had been excavated and if any remains and/or artifacts were found there.
Something is not right. This message is just to keep things from messing up down the road