I'm pretty sure this is some kind of Tussock Moth caterpillar, seen on 20th August at West Bragg Creek Provincial Park (west of Calgary). I looked at so many Googled photos late the other night and now can't remember which kinds I thought this could be. Maybe either the Rusty Tussock Moth or Douglas Fir Tussock Moth? Silly me, I should have written down which was the closest! I'd never seen one like this before, so I'm always thrilled to bits to see something new.