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"The relation of the vegetation to that of the Rocky Mountains is indicated by the occurrence of a number of relatively northern plants. Of these, Western yellow pine (Pinus brachyptera), Arizona cypress (Cupressus arizonica), Douglas spruce (Pseudotsuga mucronata), maple (Acer grandidentatum), quaking aspen (Populus tremuloides), and buckthorn (Rhamnus betulaefolia) are the more striking examples.

"The occurrence of a surprisingly great number of eastern plants, that is to say, plants which are found frequently east of the 98th meridian, is also interesting. Among the grasses are two gramas (Bouteloua hirsuta and B. curtipendula); three bluestems (Andropogon saccharoides, A. scoparius, and A. furcatus) and Gama (Tripsacum dactyloides). Among the shrubs are Clematis drummondii, hop-tree (Ptelea trifoliata), pallid hackberry (Celtis pallida), Mexican buckeye (Ungnadia speciosa), sumac (Rhus vixens and R. trilobata). White prickly poppy (Argemone platyceras), nightshades (Solanum rostratum, S. eleagnifolium), prostrate amaranth (Alternanthera repens) and sleepy catch-fly (Silene antirrhina) are common herbs.

"The surrounding plain averages about 3500 feet in altitude and slopes gradually away from the mountains. Most of the plains soil is derived from cretaceous rock and supports desert scrub such as Larrea, Flourensia, Condalia, Acacia, Mimosa, and Prosopis. In this are frequently found societies of ceniza (Leucophyllum texanum, L. minus), Parthenium incanum, and Porlieria angustifolia. Grasses are sparse in the plains, due in part to extreme over grazing and in part to desert conditions.

"On the low foothills and uneven outwash of the mountains are found relatively heavy growths of sotol (Dasylirion), lechuguilla (Agave lechuguilla), Yucca macrocarpa, ocotillo (Fouquiera), Condalia, and various cacti. The waterways support Mexican buckeye (Ungnadia), desert willow (Chilopsis linearis), western walnut (Juglans rupestris) , wild rose (Fallugia paradoxa), and Gregg's ash (Fraxinus greggii).

"In the higher foothills the shrubbery becomes denser and is less confined to waterways. On the lower mountain slopes are vast areas