PLATE 12 



Fig. 18. Burrow of the Harris ground squirrel (Ammospermophilus harrhi) 

 beneath creosote bush on desert mesa near Mellen, Arizona. The wind-worn 

 pebbles of the mesa surface are here well shown, the loose sand being con- 

 tinually removed by the prevailing winds. Photograph taken February 28, 

 1910. 



Fig. 19. Ironwood tree almost completely killed by the rising of the water 

 level in the soil at the outer edge of second bottom. A nest of the Lucy 

 warbler {Fermivora luciae) was situated 3.5 inches from the ground in a cavity 

 in the side of the trunk. Photograph taken April 12, 1910. near the Draper 

 ranch, on the California side eighteen miles north of Picacho. 



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