The idea, that the symbols are for guiding airplanes, seem to be one realistic reason. They can be also targets and test grounds for explosives, chemical and biological weapons.
After taking a closer look to US Army test ranges by Google Earth, I found a lot of similarities.
Both, in Nellis Range (NV) and Dugway Proving Ground (UT) one can find similar symbols, patterns and lines all over the areas.
I created a second Google-Map, where lots of those patterns are marked.
Their patterns are more precise and complicated as the ones found near Hanksville. Maybe those in Hanksville are older.
But until now, I haven't found any report about USAF activities near Hanksville. The following examples show, that several active areas exists in the southwest.
The mission of Dugway is to test U.S. and Allied biological & chemical defense systems; perform Nuclear Biological Chemical survivable testing of defense material; provide support to chemical and biological weapons conventions; and Operate and maintain an installation to support test mission.
Dugway is located approximately 80 miles west-southwest of Salt Lake City, Utah in Tooele County. DPG, covering 798,855 acres, is located in the Great Salt Lake Desert, approximately 85 miles southwest of Salt Lake City, Utah.
Surrounded on three sides by mountain ranges, the proving grounds terrain varies from level salt flats to scattered sand dunes and rugged mountains.
DPG includes mountains, valleys, and a large, flat, sparsely vegetated area that extends westward into the southern reaches of expansive salt flats of the Great Salt Lake Desert. In 1941, the Chemical Warfare Service (CWS) determined that it needed a large-scale chemical and biological warfare testing area. With increased population growth near the U.S. Army's Edgewood Arsenal, MD, and because of restrictions on various testing there, the CWS surveyed the western U.S. for a new location to conduct its tests. The construction of Dugway Proving Ground began in the spring of 1942. In February 1943 an airport with a 5,200-foot runway was completed.
DPG was officially established 12 February 1942, and testing commenced in the summer of that year. During World War II, DPG tested toxic agents, flame throwers, chemical spray systems, biological warfare weapons, antidotes for chemical agents, and protective clothing. In October 1943, DPG established biological warfare facilities at an isolated area within DPG (Granite Peak). DPG was slowly phased out after W.W.II, becoming inactive during August 1946. The base was reactivated during the Korean War and in 1954 was confirmed as a permanent Department of Army installation. In October 1958, DPG became home to the U.S. Army Chemical, Biological, and Radiological (CBR) Weapons School, which moved from the U.S. Army Chemical Center, MD.
In March 1968, 6,400 sheep were found dead after grazing in south Skull Valley, an area just outside Dugway's boundaries.
When examined, the sheep were found to have been poisoned by a deadly nerve agent called VX.
The incident, coinciding with the birth of the environmental movement and anti-Vietnam protests, created an uproar in Utah and internationally
Today DPG continues its role in the testing of chemical agents, pathogens, and toxins, now conducted in sealed containment chambers (rather than open air testing as in the past). Other activities at DPG include Army Reserve and National Guard component maneuver training, and U.S. Air Force Flight Test Center.
The enormous size of U.S. Army Dugway Proving Ground's Melvin Bushnell Materiel Test Facility (MTF) makes it an ideal test ground for large vehicles and aircraft, including tanks or fighter aircraft. High-tech capabilities ensure testing in the MTF can replicate real-world battlefield conditions. Test environments can include the use of chemical agents and simulants, as well as any number of interferents, such as signal smoke, fog oil, burning brush or rags. These are used in attempts to confuse the chemical detectors during testing. A technician's command can change the "weather" inside this 50-by-50-by-30-foot chamber, mimicking any number of climactic conditions. Temperatures can vary from minus 40 to 150 F while the relative humidity can range from 4 to 95 percent. Other MTF chambers include the Agent Transfer Chamber (ATC) and the Closed System Chamber (CSC). The ATC, which measures 25-by-25-by-20 feet, supports agent transfers, monitoring, and dissemination. The CSC, which is the same size as the ATC, supports small chamber and glovebox tests.
(Partially adapted from GlobalSecurity.org)
Jan 27, 2011: Misplaced vial of VX nerve agent locks down Dugway.
Dugway Proving Ground, a massive Army base in Utah along the border with Nevada, has been under lockdown for many hours now because of some kind of "national terror alert" to "resolve security issues. "Dugway is a bioweapons lab and supposedly home to secret military aerial projects. More than 6,300 sheep died near the proving ground in 1968 when a cloud of "nerve agent" hit the livestock herds in Skull Valley. Dugway is also where the U.S. Government has been testing weaponized Anthrax as recently as 1998. The Twitter feed tonight is kind of terrifying. Seven hours after the lockdown and there's still no explanation.
Gah, anyway, we have no idea what's going on. The police scanners in the area are no longer operating -- not the web streams, anyway -- and the Twitter is filled with local reporters asking for information from anybody. There are 2,000 people locked down on the base, apparently. [Salt Lake Tribune]
UPDATE: As of Thursday morning, the lockdown has ended but the whole thing remains a Total Mystery, as the Army won't say what happened. [Salt Lake Tribune]
(Partially adapted from The Salt Lake Tribune)
The findings of USAF marked metal cans show, that there was kind of army activity in the area around Hanksville, UT. But the type of signs and landmarks are different than the examples shown above. Maybe it was some kind of training area, but there is no report of such activities in the area. More resonable is the assumption, that the lines and signs have a technical reason, like mining.
 Dugway Proving Grounds - GlobalSecurity.org
 Photographs from Military Activities in the past - Togetherweserved.com
 Chemical Warfare Architecture - JF Ptak Science Books
 Twentieth Century Geoglyphs - Military Training Targets of World War II, Presented at The 80th Annual Meeting of the Society for American Archaeology, San Francisco, California. 2015