Cochise College Student Papers in Geology

Geology Home Page physical geology historical geology planetary gems

Roger Weller, geology instructor

Dragoon Mountains
Mark Alexander
Historical Geology

Spring 2006

The Dragoon Mountains are located in southeastern Arizona in the Coronado National Forest.
http://www.flashearth.com/?lat=31.842485&lon=-109.945679&z=9.8&r=0&src=2
between Tombstone and Willcox. They measure in length of about 25 miles with it highest point of 7,512 feet. The mountain range is part of the Arizona “Sky Lands” http://en.wikipedia.org/wiki/Sky_island .
The Dragoon Mountains are a fabled area which was the hideout of the Chiricahua Apaches when they were pursued by the U.S. Cavalry. The legendary chief Cochise is buried somewhere in this natural granite fortress, although the location of his grave is unknown. The Dragoon Mountains were named after the 3rd US Cavalry, known as the Dragoons. They acquired their name from the fact that they used heavy carbines rather then the usual saber and revolver associated with cavalry troops. During the late 17th and early 18th centuries, a dragoon was traditionally a soldier trained to fight on foot, but transported himself on horseback. In other words, he moved as cavalry but fought as infantry. The name derives from the dragoon's primary weapon, a carbine or short musket called the dragon. Sometimes, carbines are said to have been called dragons in reference to "breathing” fire because they expel smoke and flames when fired. Dragoons were organized not in squadrons or troops on horses, but in companies on foot, and their officers and non-commissioned officers bore infantry ranks. The flexibility of mounted infantry made dragoons a useful army, especially when employed for what would now be termed "internal security work" against smugglers or civil unrest. The dragoon regiments were also cheaper to recruit and maintain than the notoriously expensive regiments of horse calvary. However, dragoons were at a disadvantage when engaged against true cavalry, and constantly sought to raise their horsemanship, armament and social status to the levels of the horse regiments. Thus, "dragoon" had come to mean medium cavalry by the time of the early wars of Frederick the Great, in the 1740s.

This intrusion in the Dragoons is mainly granite, a coarse-grained (phaneritic), plutonic, igneous rock
rich in orthoclase feldspar and quartz.

What you are looking at is an aplite dike, the name given to intrusive rock in which quartz and feldspar are the dominant minerals. Aplites are usually very fine-grained, white, grey or flesh-colored, and their constituents are visible only with the help of a magnifying lens. Dykes and threads of aplite are very frequently to be observed traversing granite bosses; they occur also, though in less numbers, in syenites, diorites, quartz-diabases and gabbros.

     Without doubt, aplites have usually a genetic affinity to the rocks they intersect. The aplites of granite areas, for example, are the last part of the magma to crystallize, and correspond in composition to the quartzo-felspathic aggregates which fill up the interspaces between the early minerals in the main body of the rock. They bear a considerable resemblance to the eutectic mixtures which are formed on the cooling of solutions of mineral salts. They remain liquid till the excess of either of the components has separated out, finally solidifying en masse when the proper proportions of the constituents and a suitable temperature are reached. The essential components of the aplites are quartz and alkali feldspar (the latter usually orthoclase or microperthite). Crystallization has been apparently rapid (as the rocks are so fine-grained), and the ingredients have solidified almost at the same time. Hence, their crystals are rather imperfect and fit closely to one another in a sort of fine mosaic of nearly equidimensional grains. Porphyritic feldspars occur occasionally and quartz more seldom; but the relation of the aplites to quartz porphyries, granophyres and felsites is very close, as all these rocks have nearly the same chemical composition. Yet the aplites associated with diorites and quartz diabases differ in minor respects from the common aplites, which accompany granites.

     The accessory minerals of these rocks are principally oligoclase feldspar, muscovite, apatite and zircon. Biotite and all ferromagnesian minerals rarely appear in them, and never are in considerable amount. Riebeckite-granites (paisanites) have close affinities to aplites, shown especially in the prevalence of alkali feldspars. Tourmaline also occurs in some aplites.

     Aplites form dikes and irregular veins, which may be only a few inches or many feet in diameter. Less frequently, aplite forms stocks or bosses, or occupies the edges or irregular portions of the interior of outcrops of granite.

     The syenite-aplites consist mainly of alkali feldspar; the diorite-aplites of plagioclase; there are nepheline-bearing aplites which intersect some elaeolite-syenites. In all cases, they bear the same relation to the parent masses. By increase of quartz, aplites pass gradually, in a few localities, through highly quartzose modifications (beresite, &c.) into quartz veins.

The Dragoon Mountains present a perfect display of lichens attacking the granite.

Lichens are symbiotic organisms made up by the association of microscopic green algae or cyanobacteria and filamentous fungi. Lichens live on various surfaces, such as soil, wood, and rock. They are often the first to settle in places lacking soil, constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes. Some survive in the tough conditions of deserts, and others on frozen soil of the arctic regions. Recent ESA research shows that lichens can even endure extended exposure to space. Some lichens have the aspect of leaves (foliose lichens); others cover the substratum like a crust (crustose lichens); others adopt shrubby forms (fruticose lichens); and there are gelatinous lichens.

In addition, the Dragoon Mountains are a very good example of jointing granite intrusions. An intrusion is a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Bodies of magma then solidify underground before they reach the surface of the earth. Jointing is simply flat breaks along which there has been little or no movement.

The Stronghold Granite intrudes a highly deformed terrain of Cretaceous rocks. Tectonic movement in the central Dragoons is mostly towards the Northeast. Between the central Dragoon block and the southern Dragoon block is the where a major fault zone is located.

The age of the Dragoon Mountains are somewhere between the Jurassic/Triassic time period about 186 million years old. It is well worth spending the day to hike up and view the granite up close.

Dangers to be concerned about consist of the following so please be careful on your expedition.

Dehydration: Bring more water then expected. Hiking can dehydrate the body very quickly especially when exercising your body.

Spiders: Many different types may be found, the best bet is before picking up a rock or placing your hand in the nice dark hole, consider what may be lurking underneath, tying to hide from the hot Arizona sun.

Snakes: Your hearing is your best defense for staying away. You may encounter rattlesnakes, so be careful where you step and listen as you walk. Leave the I-pod home that day and listen to nature, it may save your life.

Sunburn: This is the easiest danger to avoid, wear sun block and cover as many exposed areas as possible.

Losing your way “getting lost”: Hopefully you have told someone where you going so they can look for you when you do not return home for dinner. Getting lost may take some skill in the Dragoons, because they are a small range for Arizona. Nonetheless, carry a map and a compass. If you can afford a handheld GPS system great. Turn on the cookie crumb mode so you can find your way back to you vehicle or base camp. I personally have been in these mountains several times usually by myself on a motorcycle. So venturing out alone is not a bad idea. Just keep in mind you are alone. So leave the “Indiana Jones” mentality at home that day.

Wildlife: The animals that you encounter are more afraid of you and will often flee away. Using common sense is a good tool when exploring the Dragoon Mountains. Respect the animals and they will respect you.

Travel caution: This I found a little odd. Apparently, Illegal immigration may be encountered in this area along with smuggling. It is about 37.5 miles from the Mexican boarder as the crow flies. I have personally never seen any illegal activity on my hikes. But you will see a strong presence of US Boarder Patrol so, as the sign below states be careful