Many parts of the country have definite seasons. You can look at a picture and easily guess the season by the way the natural elements look. In the desert, the seasons have their differences, but the differences are subtle, and you have to know what to look for.
I took the attached photo this afternoon in Joshua Tree National Park. In many ways, the picture could have been taken at any time of the year, and it would look virtually the same as this one. But this photo holds two small clues that reveal what season it is:
(1) the rusty-red seedheads of wild buckwheat dot the landscape; admittedly, these can persist pretty much throughout the year;
(2) the real clue, a little hard to see in this view, but it's there -- the rabbitbrush is in bloom with goldenrod-yellowish flowers. Rabbitbrush is an autumn-blossoming shrub common in many places in the West.