Spruce-tree House (pls. 1, 2)a is situated in the eastern side of Spruce-tree canyon, a spur of Navaho canyon, which at the site of the ruin is about 150 feet deep, with precipitous walls. The canyon ends blindly at the northern extremity, where there is a spring of good water; it is wooded with tall piñons, cedars, and stately spruces, the tops of which in some cases reach from its bed to its rim. The trees predominating on the rim of the canyon are cedars and pines.

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aThe photographs from which plates 2-4, 6, 8-14 were made were taken by Mr. J. Nussbaum, photographer of the Archological Institute of America.

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The rock out of which the canyon is eroded is sandstone of varying degrees of hardness alternating with layers of coal and shale. The water percolating through this sandstone, on meeting the harder shale, seeps out of the cliffs to the surface. As the water permeates the rock it gradually undermines the harder layers of sandstone, which fall in great blocks, often leaving arches of rock above deep caves. One of these caves is situated at the end of the canyon where the rim rock overhangs the spring, which is filled by water seeping down from above the shale. Another of these caves is that in which Spruce-tree House is situated. Several smaller caves, and ledges of rock harder than that immediately above, serve as sites for small buildings.

The wearing away of the fallen fragments of the cliffs is much hastened by the waterfalls which in time of heavy rains fall over the rim rock, their force being greatly augmented by the height from which the water is precipitated. The fragments continually falling from the roofs of the caves form a talus that extends from the floors of the caves down the side of the cliff. The cliff-dwellings are erected on the top of this talus.