Yes, brought our flat land Ohio horses with us to WA. One has handled the transition very well. The other not so good.
I spent all winter trying to keep my guy legged up and certainly didn't start him out at Haney Meadow. We did quite a few miles closer in to civilization before we started heading further afield.
The inclines haven't bothered him too much. On steep downhills he drops his butt to the ground and steers with his front legs.
The horse that hasn't made the transition well is older and I think the move was much harder on her than my young (4 yo) gelding. She's been sick a few times since we got out here and was just diagnosed with DLSD (or some acronym like that. It's a chronic suspensory ligament disease) so she'll never see the mountain trails. It's a shame since she's always been my best horse.