152 SYNOPSIS OF THE CACTACEZ OF THE UNITED STATES. 
The upper Rio Grande runs through New Mexico from north to south. The capital, Santa Fé, 
is not far from the river, in lat. 353°; and the town of Albuquerque is a little below. Dofiana is a 
small place on the river, above El Paso. El Paso itself, where the Rio Grande breaks through the 
mountain ranges, changing its heretofore southern to a southeastern course, is the central point of 
our Cactus region, partly from its geographical position, and partly because many of our explorers 
have made it the centre of their operations. 
The present southwestern boundary of the United States runs from El Paso irregularly westward 
through the former Mexican State of Sonora to the Colorado “of the West,” or “of California,” which 
comes from the South Pass in the Rocky Mountains, and runs southwestward and southwardly. 
Its principal tributaries rise in the east. Those most important to us are the Little Colorado, or 
Colorado Chiquito, under the 35th and 36th degrees of latitude; Bill Williams’s Fork, or Williams’s 
River, as it is lately styled, farther south; and in lat. 33° the Gila River, which rises near the 
“ Copper-mines,” northwest of El Paso. 
Proceeding from Santa Fé westward, we find the Indian town of Zuni, on the head-waters of the 
Little Colorado; then the San Francisco mountains, the Cactus Pass at the head of Williams’s River, 
and this stream itself. All this territory is at present included in the political organization of New 
Mexico, though uninhabited by whites. 
West of the Colorado, in lat. 35°, is the Mojave or Mohave River, rising in the Sierra Nevada 
near the Cajon Pass. Lower down, opposite the mouth of the Gila, the country is a sandy desert, 
extending westward nearly to San Felipe, on the eastern slope of the California Mountains in the 
same latitude. On the western sea-coast the town of San Diego is the only interesting point for the 
plants under review. 
GEOGRAPHICAL DISTRIBUTION OF THE CACTACEZ IN THE TERRITORY OF THE 
UNITED STATES. 
As to the geographical distribution of the Cactacew, our territory may properly be divided into 
eight regions, namely : — 
1. Tae ArLantic Recion, which has only a single Opuntia, and that peculiar to it. [313] 
Along the southern coast some West Indian species may yet be expected. 
2. THe Mississippi REGION, including the Western States, produces another Opuntia, which, in 
different distinct forms, extends into the third, fourth, and fifth regions. 
3. THE Missouri RecIon ; namely, the Northwestern or Upper Missouri Territory to the Rocky 
Mountains. It furnishes two Mamillarie of the subgenus Coryphantha, both extending into the 
fourth and fifth region ; and three Opuntie, one of which only is peculiar. 
4, THE TEXAN REGION; namely, the eastern and inhabited parts of Texas, westward to the San 
Pedro, and northward including the territory south of the Arkansas River. This region produces 
five Mamillarie, two of them peculiar to this district: three Eehinocacti, none of which are found 
in any other of our regions :! six Cerei (five Echinocerei and one Eucereus), all of them peculiar to 
this district: and six Opuntia, of which only three are restricted to it; among them is only a 
single cylindric Opuntia. This region contains therefore altogether twenty species, fourteen of which 
are peculiar to it. 
5. THe New Mexican Recion; namely, western, uninhabited mountainous Texas, and 
eastern New Mexico to the eastern head-waters of the Colorado of California. This region is Our 
richest Cactus district. It has furnished sixty-five species, fifty-five of which are peculiar to it, 
namely: nineteen Mamillarie (eight Eumamillarie, ten Coryphanthe, and one Anhalonium), of 
which sixteen are peculiar: nine Echinocacti, all of them belonging to this district only: sixteen 
1 Always excepting Mexico itself, south of the Rio Grande, into which many, if not most, of our species extend. 
