Lyall's penstemon is a regional endemic, meaning it's only found in our part of the world: western Montana, Idaho, and nearby Canada. It has larger blooms than most of our penstemons, and a multistem upright to sprawling habit that lends itself perfectly to steep slopes and rock gardens. 
 
Uncoincidentally, this species naturally grows on bare or rocky slopes. It prefers full sun to part shade, and doesn't want a bunch of aggressive neighbors. While this is a low water species, it lives at higher elevation so I like to provide it with slightly more water (and afternoon shade if possible) when growing it on the valley bottom. The large pale purple to pink flowers attract many bees, but bumblebees especially. The clumped stems with long narrow leaves terminating in clusters of huge flowers really set Lyall's visually apart from our other penstemons. 
 
Penstemons can be short lived, so be sure to leave some seed heads on at the end of the season.
 
Suggested companions include Alberta penstemon (actually pretty much any of the other penstemons), alumroot, stonecrop, sandwort, rush pussytoes, and cutleaf daisy (in general, rock garden type plants that won't crowd).
 
Rock wall photo: Spencer Quayle
https://www.inaturalist.org/people/noam_chimpsky, CC0, via Wikimedia Commons