Found a video of the dam being built. The fill looks to be alluvial in nature with a lot of fist sized, rounded rocks in it.
https://www.youtube.com/watch?v=hJ8Um5KJfF0
.
The spec is and was at that time 90% of aggregate has a minimum of 3 broken faces.
That is in both California Standard Specifications, and in AASHO specs too.
We have no reason to believe that anything else was followed.
It is notable that none of the people residing in Oroville that had worked on the dam construction participated in the panic evacuation. They just stayed put and shook their heads at the massive ignorance and mismanagement.
.