Just imagine all that is lost to construction ; (
I am sure they keep them closed for fear of lawsuits and crap. Sad thing is they will sit for years like that.
Contacting the owners of the big ones might be a way to go-they may be willing to let stuff go for less if its been sitting awhile
There is a landscape company in Zapata I looked up with express intent.
They had a large pile of Rio gravels in the yard, guessing 3 dump truck loads. Washed and free of caliche.
I asked if I could stretch the garden hose to the pile to wet them so I could see the colors better.
They were curious as to what I was doing and the whole staff came out to watch.
I collected a couple of 5 gallon buckets of nature's finest whilst they watched.
Obviously they had never had a rock collector in their life.
The value of tumbles ? Ah, I had brought a bucket of tumbled Rio's and handed small hand full out to each of them.
They then saw the light.
Ended up with 10 gallons of free fine agates and woods.
Being a really dirty old man I did give that fine looking Spanish-American secretary(OMG and lightning strike me dead) green and red Rio tumbles representing the color of the Mexican flag.
Sorry, I had been away for a couple of weeks and I did tell my wife I had illicit desires.
Taking it a step further I thought about paying them $50 to reshuffle that pile with their loader so new agates would be exposed.
They were starting to get bored so I moved on. As you mentioned, many people do not have a strong fetish for rocks.