We found this plant - the only one we saw - along the trail to Peyto Lake (along the Icefields Parkway, Banff National Park) on 29 August 2013. I think it has to be a species of Silene, but ID will have to wait. I think it's such an attractive flower, I would say about three-quarters of an inch to an inch across, and in pretty good shape.

Not sure, but the closest I have found in Google Images is Silene auriculata subsp. lanuginosa (Bertol.) Arcang. (Silene lanuginosa). All other species of Silene seem to have teach petal divided into two lobes, whereas this flower has the additional little white "fingers".

Later: looks like it could be Parry's Catchfly / Silene parryi.