GR translation: solid-set against the purple mountainslope

[Mike Jing]

P69.21-28  This Crutchfield here is browned by sun, wind and
dirt—against the deep brown slats of the barn or stable wall he is
wood of a different grain and finish. He is good-humored, solid-set
against the purple mountainslope, and looking half into the sun. His
shadow is carried strained coarsely back through the network of wood
inside the stable—beams, lodgepoles, stall uprights,
trough-trestlework, rafters, wood ceiling-slats the sun comes through:
blinding empyrean even at this failing hour of the day.

What does "solid-set against the purple mountainslope" mean?