Luckily, the only venomous snake in Idaho is the Western rattler (there are 3 subspecies including the Prairie rattler). They're timid and in 70 years of kicking around the desert, I've only seen a handful. A few people get bitten every year but I've never known any of them personally. Deaths are rare. The poison can be lethal but usually they don't inject very much of it. Even small dogs usually survive.
One thing I haven't seen mentioned in this thread is jewelry. If you're bitten on a hand or arm, take off anything that has to be pushed on and off, like rings. The hand will swell and a ring or bracelet can become a hazard if it can't be removed quickly.
