Carl-
If you're preference is to stay in Southern Arizona, there are a number of "sky islands" which are a series of islands that rise up out of an old sea bed, what you and I might call mountains.  To the south and east and immediately to the east of Tucson is Mt. Lemmon, which suffered the indignity of a wildfire during the last decade. I know that it devastated the little town up there, but haven't seen where the fire went...if you're in a sturdy pickup, you can head south to Florence and Oracle and take an interesting backroad up the backside of Mt. Lemmon (9157').  The LARGEST WILD sycamore trees I've ever seen were along this backroad IN a campground that I believe was called Peppersauce Cmpgd, or something like that.  Very nice campground, shaded. Dozens of sycamores. Going up the backside of Mt. Lemmon, you rise up out of the desert, and pass through several vegetation zones, ending up in a subalpine veg zone, as I recall.
Two more mountain ranges of note are the Pinalenos and the Chiricauhuas...the Pinalenos are north of Willcox (which is on I-10 East heading towards New Mexico border), and is home to the Mt Graham (10720') observatory, and again a subalpine veg zone. South of I-10 are the Chiracauhua mountains (9759') with a mountain road that ascends to a pass (high as you're going to get without hiking) and down into Paradise and Portal...this area is incredibly interesting geologically and biologically, with very special habitats...birders love this area and well they should...lifelisters make it a 'must-do'.

But it's hot as heck down there, and I'd personally recommend running up from Phoenix onto the Moggolon Rim, so you can pass through the largest contiguous ponderosa pine forest in the world.  There are some big trees still left (Long Valley I'm told has some, and is in between Strawberry and Happy Jack which is a nice ponderosa forest road that will take you into the back way to Flagstaff).  Immediately to the north of Flagstaff are the San Francisco Peaks (12,633', rising above the town of Flagstaff at 6500'), with a road that accesses the sky area at around 9000', with trails that access the north side...Schultz Road crosses over the base from east to west on the south side of the Peaks...the Peaks were made famous among ecologists in 1890 by C.H. Miriam who recognized that the vegetation zones that occupied the Peaks had latitudinal equivalents that ranged from Sonoran desert to alpine.

These vegetative communities represent a relict alpine tundra flora definitely related to the high peaks tundra of the Rocky Mountains north and northeast (Moore, 1965). Twenty of about 50 species of the alpine tundra flora on San Francisco Peaks are arctic-alpine disjuncts that also live in arctic tundra zones. Fifteen of the 20 are circumpolar, growing in Arctic Eurasia as well as Arctic North America. Moore (1965) believed that at least 90 percent of the alpine tundra vascular species on San Francisco Peaks migrated from the north during Pleistocene time, possibly as recently as 65,000 to 75,000 years ago, coinciding with the last period of glaciation described by Sharp (1942). Updike and Péwé (1976) provided evidence of more recent glaciation. However, this last glaciation in the San Francisco Peaks was fairly limited in areal extent. Moore (1965) suggested further that relict alpine tundra on San Francisco Peaks has been losing its true alpine tundra character for at least 10,000 years.

Spruce-alpine fir forests cover about 97,130 ha (240,000 ac) on and around the summits of the highest mountains, including San Francisco Peaks and the Chuska, White, Pinaleno and Chiricahua mountains, and on the large summit area of the Kaibab Plateau. These Rocky Mountain forests reach their southernmost extension in Arizona and New Mexico (Dye and Moir, 1977). Spruce-alpine fir forests generally lie between 2,430 to 2,730 m (8,000 to 9,000 ft) and extend to the mountain summits, except for San Francisco Peaks where the upper limit is approximately 3,490 m (11,500 ft). The mean annual precipitation ranges from 760 to 1,140 mm (30 to 45 in), much of it as snow, and exceeds mean annual potential evapotranspiration (Beschta, 1976).

Seven coniferous and one deciduous species variously mixed characterize these forests. The principal boreal conifers are Engelmann spruce, blue spruce, corkbark fir, white fir, Douglas fir, bristlecone pine and limber pine. Quaking aspen is the dominant deciduous species, both intermixed with various coniferous species and in pure stands. Dense overstories common to these forests severely limit or prevent growth of herbaceous vegetation. Quaking aspen is considered to be a seral species that invades an area following a disturbance such as fire.

Moir and Ludwig ( 79) have classified the Lowe and Brown (1973) spruce-alpine fir forests into eight spruce-fir and 11 mixed conifer habitat types based on the concept of Daubenmire and Daubenmire (1968). The dominant climax species within the spruce-fir habitats are either Engelmann spruce or corkbark fir. Climax dominants or codominants in the mixed conifer habitats include white fir, blue spruce and Douglas fir. Kuchler's (1964) southwestern spruce-fir forest and spruce-fir-Douglas fir forest zones are included within the spruce-alpine fir forest zone on the vegetation map (Plate 11).  

This from http://southwest.library.arizona.edu/azso/body.1_div.4.html
as well as this probably helpful summary of AZ spruce-fir forest species:  

But if I had only a couple of days, and again a sturdy truck or passable SUV, I'd drive directly north for hours and hours and go to the North Rim of the Grand Canyon.  You can take a back road (if it hasn't been made a wilderness yet) that accesses Fire Point, Swamp Point which are in very much undisturbed classic ponderosa pine old-growth forest, and to really see them with the most minimal disturbance, drop down from Swamp Point, down through a saddle to the west, and up to the Powell Plateau, where the Plateau is isolated by the hike down and up, and by the relatively remote location...much of the research on ponderosa pine fire behavior has been done there because of its uniquely undisturbed state. Otherwise, just taking state highway 64 down from Jacob Lake (best cookies at the bakery there, and the thickest best milkshakes in ALL of Arizona). br> Hope this helps, it's been fun bringing back up great memories of a great place.

you've a wonderful opportunity ahead with the only negative prospect being a lack of sufficient time to do Arizona justice!  Check out following URL:

http://www.azarboretum.org/bigtrees/June2004updates.htm

which details (as of 2004) 89 species of champion big trees in Arizona, with some found by a one-time member (now passed away) Bob Zahner (may he rest in peace at the base of his champion ponderosa pine!). Turns out the Arizona trails only Florida in diverse number of species, if recall serves me, on the national register.

Yes, Arizona is a state that likes its traditions, and its foresters and tree hunters traditionally use the tangent method...I'm sure there are exceptions, and it's a feather in ENTS' hats that you're one of them. Go out there and kick some big tree butt!

-Don

PS:An endemic population of bristlecone pine exist on the top fourth of the San Francisco Peaks...and to my knowledge, nowhere else in Arizona

Edward Frank wrote (August 13, 2009):

Carl,

If you are going into the desert you might notice the crust on top of the soil.  That is what keeps it from becoming a loose sand deposit.  This is a cryptobiotic crust.  They are kind of neat.  Check out this link for information:  http://www.mineralarts.com/artwork/cryptos.html  Here is an excerpt for the page:

  CRYPTOBIOTIC CRUST is also called BIOLOGICAL SOIL CRUST.
  These are communities of cyanobacteria, green algae, lichens, mosses, liverworts, and microorganisms that colonize the surface of bare soil.  "Cryptobiotic" means "hidden life."  Crusts often go unnoticed unless they are very extensive or colorful, and some do not even look alive.  But they are vital to the health of soils and ecosystems.  Cryptobiotic crust is best known (and probably most studied) from the protected lands of the national parks of the Colorado Plateau, where it forms dark lumpy patches on the red soil.  But it is equally important to desert, prairie, and tundra ecosystems, and also colonizes bare ground in humid temperate environments.  The most complex and spectacular "old growth" crusts take decades to develop.  They are miniature forests with dozens of species of cyanobacteria, green algae, mosses, and lichens over a dark layer of organic-rich soil.  The damp soil is alive with earthworms, snails, millipedes, insects, and microorganisms, and nourishes grasses, wildflowers, and even trees.

So you might be seeing some old-growth crusts.  I am looking for detailed reports of your exploits.

Ed