Thanks for the photo. I have been telling people about this type of situation for 40 years, many questioned this but you can see in the photo it happens.
The beaches with just round rocks roll around easy and getting sunk in happens fast. With slope or grade it is worse. Over the years when driving the coastline, I will take the long way around these areas.
It is good to see you had help when you needed it. It will be firmer where the sand holds the rock from moving as easy.
Your having a Baja Adventure now!