Abstract Military geology and national security projects are comparable, achieving their raison d'etre in support of national goals, military operations, and the systems that support them—all for vital national interests. The application of geoscience to these ends, especially engineering geology, has occurred from pole to pole and included every conceivable environment and natural condition. In the conduct of such projects, the geosciences have advanced, and vice versa. Desert trafficability, most notably regarding playa surfaces, is temporary and variable and not a persistent condition as some early authors believed. Playas in Australia, Iran, and the United States show that saline efflorescence is removed following surface water dissolution and subsequent deflation, resulting in very hard crusts. Magadiite, a hydrous sodium silicate and possible precursor of bedded chert, was first discovered in North America at Alkali Lake, Oregon, during a military project. Pleistocene Lake Trinity, a small and mostly buried evaporite basin in the northern Jornada del Muerto, New Mexico, was discovered during exploratory drilling in support of a military test program. The Strategic Petroleum Reserve (SPR), operated by the U.S. Department of Energy, has underground cavern storage of ~600 million barrels of crude oil in five Gulf Coast salt domes. The geologic characterization of the SPR sites is a major component of these comprehensive engineered works—unparalleled in modern times and on a comparable scale with the Panama Canal. Numerous studies of salt-stock heterogeneity, salt-karst features, and structural and physical attributes of salt deposits are broadening the database for use in the commercial storage industry. Geologists serving in military and national security endeavors are fully functioning members of the project technical teams and have made significant advances to the geosciences.

Abstract Playas are among the most common of desert landforms, with more than 50,000 worldwide and with great variation in size and physical characteristics. They range from a hectare or less to hundreds of square kilometers, and they may support aircraft landings or be totally impassable to land vehicles. Because they possess distinctive physical attributes and are common elements of arid and semiarid landscapes, which occupy nearly 30% of the Earth's land surface, they have had significant effects on military history and operations for centuries. This significance is not apt to diminish. The single most important determinant of playa-surface conditions is the combination of surface and ground-water hydrology. Playas with ground water that is sufficiently deep to preclude capillary rise favor hard surface crusts. Prolonged capillary or direct ground-water discharge in arid environments readily builds up evaporite mineral assemblages including halite, gypsum, and calcite. Changing hydrologic conditions resulting either naturally or from human activity, for example, ground-water extraction, can result in alteration of relief and surface hardness of playas over both short- and longer-time spans. Military use by ground forces includes both expeditious and evasive maneuvering of ground vehicles. Air and spaceborne vehicles, including fixed and rotary wing craft and spacecraft, have used numerous playas in their natural state as landing platforms, and many other playas are readily available in remote, unpopulated areas of the globe. Future uses are apt to take advantage of the unique attributes of this arid-region feature—the flattest of all landforms.

Abstract The military environment of the post–World War II years was dominated by the principal threat of air and missile attacks over polar routes between North America and the former Soviet Union. The extremities of the arctic environment demanded unique adaptations to normal military operations, which provided military and engineering geologists an opportunity to exercise a broad range of technical applications. New knowledge and skills in ice physics and engineering, glaciology, arctic geomorphology, meteorology, oceanography, and permafrost engineering were all relevant, often requiring on-the-job learning. Such adaptability could be needed in the future and would once again challenge military geologists.