The Sierra El Humo are the western-most true Madrean "Sky Island" mountain range. They are about 70 km southwest of Sasabe, Sonora and rise from the Sonoran Desert floor sharply, especially on the southern end. The El Humo are one of the more remote sierra with no pavement or towns within many miles.
There are some decent patches of oak in north facing canyons and slopes. Blue Oak (Quercus oblongifolia), Emory Oak (Q. emoryi) dominate, but is replaced by Arizona oak (Q. arizonica) at some higher elevation locations.
Apparently there is a perennial drainage with fish flowing off the north slope of the mountain (pers. communication with ranch owner). This extremely isolated potential fish population should be examined at some point.