That mud is what they use, on drilling rigs it also expands quit a bit. Their is a fair amount of it in Wyoming and West Texas as well. You can also buy it in roofing supply stores to temporarily fix leaks on flat roofs. We bought it as a powder in bags, and made gobs of money fixing leaks with it.

And to be fair anytime we were miles back and it started raining, we left as soon as it started to rain.