Not rain gear specifically, but here is something I experienced on my first elk hunt.
I went on a bow hunt in southeast Idaho mid September. The weather was beautiful, no rain, 45 degrees at night, and 70 degrees in the afternoon. It was perfect for camping and hiking. The mornings had a heavy dew, and the wet sage and scrub oak brushed my shins as I hiked and stalked. My boots were water proof and fought the good fight, but my feet got soaked from the socks down. By the fourth afternoon, I was sitting on a sunny rock with my boots off because I had run out of dry socks.
That is how I discovered the value of waterproof gaiters, and I would recommend having a pair, even in the high desert.