We took a grand tour one day, travelling all the way to southern end of the park,
to Cottonwood area and on out into civilisation and Palm Springs.

As you go south-east, you travel into the "transition zone" - the area between
the Mojave desert to the west and the Colorado desert to the east. This area
was even more arid, but also filled with strange small pockets of vegetation.
The cholla growing here were densely packed, but only grew in abundance in
that one spot. 

At the base of many of the plants were pack rat nests. These are
desert dwellers who protect themselves by making elaborate nests of cholla
bobbles. There are secret ways in, but only the pack rat knows them. While
wandering in the cholla garden, I heard some pack rats squeaking in their nest.

A few miles down the road, there was an ocotillo patch - ocotillos grown long
spikey arms, with brilliant red flowers on the ends.