The distance a snake rattles from varies across the west. Whatever breed is in the Utah book cliffs will start rattling 100 feet away - a bunch of us Wyoming boys were quite impressed. As we got closer to it, at 10’ away the snake was not having any part of it and sort of bluff charged then ran away. That was the only snake any of us didn’t want to have anything to do with, even though it had a big rattle. If you got within 5’ I have no doubt it would try to bite. We ran into a handful of others that were just the same - they were easy to spot from the rattling at distance.
Most Wyoming, Idaho, and Colorado snakes won’t bite unless you put yourself close enough for an easy strike - I’ve never had one even bluff charge. Rattling won’t start until you’re less than 5-10’, and often a snake won’t rattle at all and just coil up and look at you. The rule of thumb is don’t step or put your hand anywhere you can’t see if a snake is within striking distance. I walk two feet ish from brush as do many people and almost never have problems, but that’s not always possible so I may slow down and look closer as I go to up my odds. The guys that get bit more than once have habits of putting hands where they can’t see.
The ones I’d watch out for are the babies and adolescents - something the diameter of a pinky will gladly bite you and the tiny fangs might not feel like much. Snakes the size of a thumb can be hard to see.
The only snake bite in 10 years of wildland firefighting and a lifetime of messing around in the foothills and sage flats was when we were bushwhacking through some 4’ to 6’ brush of some kind on Casper Mountain near Casper, Wyo. One of our guys started feeling bad, had what looked like a spider bite on his upper arm, and we drove him to the hospital thinking it was an allergic reaction to a spider. Turned out a baby snake was up in the brush and only got one fang in him. I’ve never seen a small rattlesnake up in brush before, during, or since, and wouldn’t have believed it if I wasn’t a few feet from him when it happened, but I’m much more careful now.
As grade school kids we’d lift our feet off the bicycle pedals and laugh as we sped by young snakes coming out of a snake den that were trying to strike at us. I’m sure a lot of boys end up in the ER playing with snakes. Lol