All three have similar layouts. Substation Osprey is on a tall hill with a Hard locked storage area underneath the main office area, with some crates and a toolbox. The entire building is marked with the chalk-white handprints of the Dead Horses scouts.
When Follows-Chalk is traveling with the Courier, reaching this location will reveal nearby map markers and inspire a heightened sense of awareness (Perception +3) for three minutes with the Well-Stacked Cairns perk. The map markers revealed here include Cueva Guarache, the Zion Ranger station, and Caterpillar's Mound.