IThe thing I have seen with rattlesnakes are that if you a lot of cactus and rat dens, you have rattlesnakes. .
Absolutely. You hit it on the head. If there is a good 'food source' they will be there.
A friend of mine's Dad had a small place down in Encinal (600 acres). He had some parts of the property 'chained off' (this was back in the 70's before all the neat brush mulching equipment they have now). All of the Cactus and Mesquite, etc... would get pushed up into piles (rows really) about 6' high. There were big rats (Norway rats I think) living all throughout those brush piles.
I never saw so many Rattlesnakes on a South Texas ranch and I've been on quite a few. We would go down there in late March or Early April (depending upon the weather) and drive the ranch roads the first couple of hours after sundown. We had a big wooden box with a locking lid in the back of a Jeep and we would catch the snakes we found crossing the sandy roads.
It was not unusual to catch upwards of 20 snakes (no joke) in just a couple of hours. Sometimes we would make a round and come back only to see where several snakes had crawled over our tire tracks, so were missing some as well.
Another place we could find Rattlers in the daytime was in the big Pear Flat on the place. Of course, that took a lot of walking and looking and we had to put those snakes in a pillow case and tote them back, so we did more driving at night. Much more fun to drink beer and cruise for snakes than get right out there amongst them.
We would sell the snakes we caught (live) to a guy who owed a Western Store in Austin (where we lived). He would make all sorts of things from their skins and was paying pretty good money for them (at least for a couple of 20 yr. olds).
I have run across snakes while hunting on other ranches between Cotula and Laredo but 'habitat' makes all the difference.