Comprehensive car insurance covers damages from an "act of God," or events that are not caused by a car driving into something else. An "act of God" can include things like damage from a heavy tree branch falling on your car. Since you have no control over when or why a tree branch would fall on your car, this kind of accident would be covered under your comprehensive policy.
Idaho is pretty sparsely populated and mainly rural which leads to lower car insurance rates. According to World Atlas, Idaho has the seventh least population density in the country. There are roughly 20 people for every square mile. Wide-open spaces with few people mean fewer cars out on the road and fewer accidents, everything an insurance company loves.
Collision coverage is limited to the actual cash value of the vehicle, and requires a deductible, which is the amount you'll need to pay before receiving benefits. Higher deductibles lower your premium but increase the amount you must pay out of your own pocket if a loss occurs. Ask yourself how much you would be willing to pay on short notice in order to save on your premium, or talk to your agent.