In Arizona, where is the dividing line between the Sonoran & Chihuahuan Deserts?

[nmdesert]

Originally Posted by eddie gein

I've lived in both Chihauhuan desert (Alpine, Tx) and Sonoran (Tucson) and also in Willcox. The Sulpher Springs Valley where Willcox is reminds me very much of Alpine and Marfa Texas except for the sky Islands around Willcox. Pretty much grassland.

As far as Saguaros go, they only grow naturally in a certain elevation range. I've never seen them even on the east side of the Rincons really. So I'd say drawing a north south line on I 10 it's about Mescal/J-6 where they are completely gone.....

On the return trip home from Tucson last week, I wanted to verify some saguaro-like shadows NW of Benson seen on Google satellite view. I took Ocotillo Rd north over 10-12 miles, which is over 3 miles beyond the end of pavement. Past the pavement there were a couple saguaro spears (no arms) on hills to the east, and west of the road a single saguaro with a couple arms. Many more saguaros with multiple arms occurred where the road bent to the east, and steep hills came SE of the Rincons. Not one palo verde in sight, just Chihuahuan-form creosote bushes and dried up mesquites and acacias. And a good number of saguaros had evidence of dieback from winters at least a decade ago.

My impression of Benson is that it's easily as warm as El Paso but winters are less susceptible to cold than El Paso or anything until the Big Bend. The weather records don't show that so well, though.

Speaking of palo verdes, the Arizona state tree is the blue palo verde / Parkinsonia florida. While absent NW of Benson where I drove, it grows occasionally N of Benson and also in the lower, warmer valley area around Bowie and San Simon. A few not far west of the NM line, by the ADOT rest area...all low, shrubby, and spreading like those around Safford.

I'll post some photos from that and a previous trip.

[nmdesert]

Originally Posted by eddie gein

I've lived in both Chihauhuan desert (Alpine, Tx) and Sonoran (Tucson) and also in Willcox. The Sulpher Springs Valley where Willcox is reminds me very much of Alpine and Marfa Texas except for the sky Islands around Willcox. Pretty much grassland.

As far as Saguaros go, they only grow naturally in a certain elevation range. I've never seen them even on the east side of the Rincons really. So I'd say drawing a north south line on I 10 it's about Mescal/J-6 where they are completely gone.

I don't recall any around Willcox when I lived there.

Willcox is too cold, though there's a known stand of jojobas on the west slopes of the Dos Cabeza Mountains east of town.

Almost forgot - in March 2021 someone took me on a drive over Redington Pass into Redington, then south. I'll find my photos of that and post. There were a few tiny saguaros at almost 5,000 ft under a couple oaks near the Arizona Trail crossing. Just below that a few saguaros with arms were seen in several locations, all small though.

Late afternoon we approached Redington, and it was very Sonoran Desert-looking. Foothill and blue palo verdes with many saguaros, many with arms and little to no damage evident. I recall many jojobas, though the creosote bushes were a mix of Sonoran and Chihuahuan ecotypes / forms. Both sides of the valley. But night fell long before we drove south into Cascabel and onto I-10, where we could only pick out a couple saguaro silhouettes on the hills east of the road.

[Calizonan]

As an amateur naturalist I feel qualified to throw in my two cents.


The natural range of the saguaro, indicator plant of the Sonoran Desert, ends at the east foothills of the Dragoons (they are pretty scarce here). However, the greater Sonoran Desert climate (reliable summer monsoon between late June and late August, with very little before or after) extends out to the Chiricahuas or so on the state line, as does most of the other Sonoran-type fauna. Once you get into New Mexico on east in the Chihuahuan Desert, the monsoon is much more scattershot and unreliable; you can get a gully-soaker in May and then nothing until September, for instance.



I would put the dividing boundary at around the state line, albeit perhaps between Willcox and the state line one could call a transitional zone.