It would be hard to find a more ideal location for native plant diversity than right here in

southern Arizona.  High forested mountain ranges are separated by low desert expanses,

isolating the mountains and their plant communities, which often differ considerably from one

mountain to the next.  The proximity to Mexico, the Sierra Madre, and the tropics also results in

enhancing plant diversity, and the summer rainy season or Mexican Monsoon puts on the

finishing touches.  The rains, which usually begin in June or July, result in a second season of

wildflowers after they are finished blooming for the year everywhere else, and this time they are

quite often different from the spring flowers and more characteristic of Mexico.  Having two

flowering seasons tremendously increases plant diversity in the Southwest.  As a result, Arizona

has over 3500 species of plants and is the only state having both tropical and alpine plants.  It

is also home to the largest continuous ponderosa pine forest in the United States.  The highest

peak rises to 12,670 feet, well above timberline, in the San Francisco Mountains, and the

lowest elevations are about 100 feet above sea level in the Yuma area, where the Colorado

River is about to flow into the Gulf of California.  The low deserts are famous for their extreme

summer heat, but the mountains are often cooler than the Canadian border in the summertime.

The Southwest includes much more than Arizona though, extending from Texas to California,

and to the north and south it is certainly not confined by political boundaries.