and U.S. Army
Earth Science Applications, National Training Center, Fort Irwin

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Environmental Change Studies at Fort Irwin

Comparing historic photographs with modern ones allows us to describe changes in the environment. The earliest photographs available were taken in 1947, after General Patton's manuvers in the desert but before a renewal of activity at Fort Irwin. Several times of repeat photography are available. 1983 photographs show significant changes, mostly as widening of alluvial washes and more bright-colored dust and sand deposited northeast of the Main Post and Bicycle Lake.

Digital Orthophoto Quadrangles (DOQs) prepared from images taken 45 years apart

Showing changes in the landscape and land use

The images below represent the main operations base of Fort Irwin and Bicycle Lake (a dry lake or playa) at two different times, 1992 and 1947. Then digital images are constructed with 1-meter resolution and are geographically rectified; that is, they are stretched to match the topographic map (the southeast quarter of the Fort Irwin 7.5-minute quadrangle).

The DOQs illustrate many changes in the area over the 45-year span between images. The images can't be compared directly because of the different photographic techniques used. The 1947 image is from photographs, that were scanned and merged, whereas the 1992 image is from digital data- a single band of an infrared data set. In addition, differing sun angles and vegetation differences due to different seasons contribute to the differences in the images.

1947 Download 182 kb gif file	1992 Download 161 kb gif file

What can we see that has changed?

• At the main operations base, many more buildings and streets show in 1992.
• A water diversion ditch is present around the north end of the installation in 1992.
• A landfill was constructed east of town next to the mountains by 1992.
• Big differences can be seen in the disposal of waste water. In 1947 several outlets of water east of town created dark vegetation stirpes along stream courses. By 1992, waste water was used to irrigate a broad area farther south, the dark area near the lower edge of the image.
• Bicycle Lake has more constructed airstrips, diversion berms, and ditches in 1992.
• A profusion of dirt tracks and roads can be seen in the 1992 image. The tracks are most evident as scars on dark-colored alluvial fans.
• Many light-colored slopes in the mountains east of the base in 1992 are not visible in the 1947 image. These light areas are covered by windblown dust and sand, which probably was deposited after wind erosion in the vicinity of the operations base where vegetation is reduced and vehicular traffic disturbs soils. Old sand deposits were present in the 1947 photographs, so this wind erosion and transport and deposition is not a new process. Rather, it seems to have increased in direct response to increasing human impacts at the main operations base.
  

Historical digital orthophotographs can allow precise analysis of environmental change. USGS is now constructing digital orthophotographs for much of the Mojave Desert with modern images. It also has constructed pairs of images, from modern and 1947 photographs, of other parts of Fort Irwin and Joshua Tree National Park. These pairs can be used to quantify changes over nearly 50 years.

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Tortoise habitat predicted from geologic materials

Geologists have noted for at least a decade that tortoise populations seem to be much more robust in areas underlain by weathered granite and its erosional products of sand and gravel. In fact, specific kinds of granite appear to be favored, kinds that can be easily distinguished in the field and by remoting sensing, using processed satellite imagery.

Intensive studies in a tortoise preserve along the south side of Fort Irwin are yielding information on this interesting creature and its habitat.