Sonoran Desert Region: Yuman District. 635 
Chaparral Formation. A chaparral of oaks extends back to the mountains. It is com- 
posed of Quercus undulatus mixed with Arctostaphylos tomentosa, A. nevadensis, A. pungens, 
Acacia!Greggü, Zizyphus lyeioides, while underneath were growing Hedeoma Drummondii, Verbena 
ciliata, Mentzelia Wrightii, Hilaria rigida, Bouteloua racemosa, Muhlenbergia texana, and several 
species of Eriogonum. Here and there were Yucca baccata and Agave Parryi 
Canyon Formation. The canyons which cut into the Colorado Plateau 
and are open to the desert below are distinguished by the presence of Ouercus 
Emoryi, Alnus oblongifolia, Platanus racemosa and on the steep slopes Funz- 
perus californica var. utahensis, F. pachyphloea, Pinus monophylla and Canotia 
holocantha. Higher the canyon sides are lined with Aguzlegia chrysantha asso- 
ciated along the banks with Nicotiana attenuata, N. trıgonophylla, Mimulus 
luteus, and many perennials. Higher still where the canyon stream is shut in 
by almost perpendicular walls of rock, grow Mimulus cardinalis, Mirabilis 
multiflora, Heuchera parviflora and Pteris aguilina in large masses. 
The Foothill Formation consists of an association of Zarrea mexicana 
(= Covillea tridentata), which grows west of the Colorado river bottom in the 
gravel hills with Fouguiera splendens, Olneya tesota, Prosopis juliflora (occa- 
- sional) and Parkinsonia Torreyana, Agave, Nolina, Dasylirion, Opuntia species 
and EZurotia lanata. If we ascend the foothills, on which grow Fumiperus 
monosperma and Pinus edulis, during the dry season, we encounter Dicoria 
Brandegei, Oxytenia acerosa‘), Tetradymia canescens, Yucca baccata and 
angustifolia, Mamillaria vivipara, Cereus Engelmannti, Opuntia basilariıs, 
Ephedra antisyphilitica, while in the wet season are found Lupinus capıtatus, 
Mirabilis multiflora, Riddelia tagetina, Zinnia grandiflora, etc. 
The natural cattle ranges of the valleys and valley slopes were occupied by Eriochloa 
polystachya, Chloris elegans, Eragrostis neo-mexicana, Panicum obtusum, Chaetochloa composita, 
Bouteloua oligostachya, B. polystachya, Andropogon Torreyanus, Hilaria, mutica and H. Jamesii 
associated with Plantago fastigiata, while the most important grasses on the open mesa 
range are Hilaria mutica, H. Jamesii, H. cenchroides, Bouteloua oligostachya, B. polystachya, 
B. eriopoda, B. curtipendula, Pappophorum Wrightii and in depressions where the 
mulates after summer rains are Chloris elegans, Eriochloa polystachya, Panicum obtusum, 
num, Andropogon Torreyanus, Eragrostis neo - mexicana. The grasses found on the RT 
portions of the river bottoms are: Sporobolus eryptandrus and Chaetochloa composita. 
The mountain range?) presents a characteristfe appearance because the higher elevations 
receive a more liberal supply of moisture. Here without forming a sod are found Andropogon 
Contortus, A. leucopogon, Elionurus barbiculmis, Bouteloua bromoides, B. oligostachya, B: eurti- 
pendula, Triodia mutica, Eragrostis lugens, Muhlenbergia gracillima, M. Porter and Epicampes 
rigens, 
Desert Sand Hill Formation. On dry sand hills of the desert grow 
Coldenia Palmeri, Psathirotes annua, Hyptis Emoryi, Triodia pulchella, Erto- 
gonum inflatum, Chorisanthe rigida, Mamillaria barbata. On stony declivities 
are found Larrea, Yucca brevifolia, Atriplex canescens, Opichiia TOOSTESER 
and Echinocactus cylindraceus. 
Bot. Gaz. XLVII: 216— 223. 
ı) PnırLips, F. J.: A Study of Pinon Pine. 1). $. Burcan Plant Industry Bulle- 
2) Grirrirus, Dayıp: Range Improvement in Arizona. 
tin 4: 23. | 
