I'll be the 25th guy to say just be cooperative with them. Trust me, my uncle is a cop, and it's not fun for him to bring kids in and write citations and fines. They want to resolve the problem as easily as possible. A simple "sorry sir, we didn't think it would pose a problem" will work fine. Clean up and leave. As long as he didn't catch his wife sleeping with his neighbor that morning, you should be fine.
Then hopefully you can find a different rail, because it's not good when the same cop finds you more than once. Most cops don't really deal with skiers skiing in a city, so stuff like that sticks out in their mind.