There’s signs posted in advance that say something along the lines of “Speed Enforcement Camera Ahead”. The only reason they’d be a surprise is if you’re not paying attention to signage. They’re in the mountains, but I’ve mostly seen them out in the flat eastern parts of Colorado where the roads are mostly long straight stretches over flat terrain. Which makes sense, since that’s where it’s easy to speed.

I know that Colorado does this as well. Probably other states in the USA do too. https://www.codot.gov/programs/speedenforcement