Fantastic photo, thanks for doing the primary-source research.
Appears to be resting on a C&S-origin flatcar, and the long-snout auto, roundhouse, and misty fjord mountainsides are compelling background details.
Caboose 556 was not rebuilt by the D&RGW before its sale to the SN, so retained the early frame style with frame joists & couplers below the siding/endbeam level, hence the high-riding stance. On this side view this frame is clearly visible on the left side of the caboose, but the right side is resting on its endbeam. For a rebuilt, flush frame D&RGW caboose, this would not necessarily indicate frame damage, but in this case it must have been catastrophic. She was fortunate to persist after this as a shack with very interesting provenance.