One of the rare works in the collection with a written title in Sidney's own hand, inscribed in small neat lettering at the lower margin: "Stormy Mountains, White Bear Lake, Colorado." The title locates both place and subject precisely — this is a specific mountain seen in specific weather, painted on location or closely from memory and observation.
The work is among the finest landscape watercolors in the collection. The mountain rises steeply from the lower edge — green slopes giving way to rock faces in blue-gray and teal, the peaks jagged and geologically specific. Above, the sky is the painting's dramatic center: a large gray-blue storm cloud mass rises from directly above the mountain, dark and swelling, threatening the clear blue sky that brackets it on both sides. This cloud is not a generic cloud but this cloud, painted with the understanding of a sky-watcher — the granular texture of the dark mass, the soft edges where it dissolves into blue, the slight pink light at its base suggesting a sun still shining somewhere beyond frame.
The mountain's vegetation is handled with Sidney's characteristic dotted and stippled marks — each cluster of trees a few dark touches of color — giving the slopes a textured depth without over-describing. The snow or pale rock passages at the peak are left as near-white paper, the watercolorist's essential restraint.
This is plein air watercolor at its most classically accomplished — the kind of work that demonstrates Sidney could have had a successful career as a landscape painter alone, had he chosen that path. He chose something wider and stranger. But this is the foundation.