...the plant is dogbane (Apocynum androsaemifolium) which grows at mid-elevations and higher throughout much of the Sierra Nevada. Like milkweeds, it's often a great insect magnet when in flower.

[Perhaps it's worth noting that the milkweed family, Asclepiadaceae, has recently been subsumed within the dogbane family, Apocynaceae, by various plant taxonomists...including the editors of the current edition of the Jepson Manual for the California flora.]