I live in Aurora, about two blocks from the northeast corner of Cherry Creek Reservoir. The rattlesnakes are Western or Prairie Rattlesnakes and the biggest ones that I have actually seen have been about 3 feet, although they do get bigger. I heard that one of the neighbors on the other side of our subdivision had a 5 footer in their backyard. I've had three 3 footers in my back yard-hence my concern with getting my dogs snake trained. I've seen easily a dozen rattlers on the bike trail that runs along the Cherry Creek emergency spillway from Parker Road to Chambers Road, but none in the last two years. While walking our two labs in our neighborhood at dusk in September, we came across a 2 footer in the road about 3 houses down from ours. Luckily we saw it. Usually in the summer if we are walking at night we bring a flashlight.
Interestingly, as many as I have seen and heard, I still don't always immediately recognize the sound of the "rattle". It's really not a rattle but a high pitched buzz, similar to a 17 year locust (Cicada). I had one rattling at me that was coiled in the rocks just off the edge of my deck one night. The dogs were acting strange and had come back up on the deck from the yard. I followed them and then stopped once I got on the deck when I thought I heard a noise. I stopped and couldn't hear anything. I took another step and heard the noise again but still didn't identify it. I stopped and the noise stopped. When I took another step the noise started up and I finally realized it was a rattlesnake. I stopped and cautiously looked around. I saw the snake coiled up in the rocks about one foot from the side of the deck and about 4 feet from where I was standing, including the 18" height of the deck. Time to get a rake and shovel.
The dogs remembered their lessons well.
POL