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Finding backcountry water is essential. Recognizing potential wild sources, terrains of opportunity, can be an exercise in counter-intuitive searching. Common advice suggests searching the local low spots, ravines, arroyo’s, washes, and so on for low seeps, springs, and shallow groundwater exposed in hand dug wells in stream meander sand bars. These are usually higher probability locales than local high spots nearby. Weathering pits are one important exception. Weathering pit water holes have saved lives! Weathering pits are unique terrain features found on upper surfaces of rock masses rising above local terrains, places offering a drink along with a view! Worldwide, native peoples have sipped water from weathering pit water sources for millennia, from Apaches of the American Southwest to the Aborigines of Australia.

Weathering pits commonly form on disintegrating, deeply weathered remnants of huge crystalline bedrock masses, commonly granite and other granite-like igneous rocks. These mounds and hills of giant fitted boulders called tors are recognizable when seen from miles away, a boon for errant arid country wanderers running low on water.

As you approach, tors look like huge piles of boulders including many that fit together along rounded cracks like worn puzzle pieces. The cracks are called rock joints. The coarse sand-like sediment, disintegrated granite, filling the low spots is called grus. Tors are the weathered and eroded remnants of giant igneous rock bodies called batholiths, stocks, etc. by geologists, which formed long ago deep under ground as large pools of magma cooled slowly at depth. Eons of erosion of overburden eventually exposed the crystalline bedrock formation at the surface. Unburdened by deep overlaying rock formations, the granite body expanded and began to weather. The patterns of regular cracks formed due to stresses in the expanding rock mass near the surface, these are the rock joints. Weathering occurs more rapidly along cracks, causing rounding of edges. More erosion resistant than surrounding rocks, the crystalline bedrock formation is left elevated above local terrain as surrounding formations weather and erode more quickly, deflating surrounding terrain. Tors are erosion remnants.

Weathering pits can be found on some sandstones and other massive bedrock outcrops, too, wherever massive bedrock forms near-level surface exposures. Weathering pits begin forming when water pools in low spots. Pooled water speeds up chemical and mechanical weathering–the pool deepens–a positive feedback loop causes water to remain longer as pits deepen. Wind can increase size and depth of pits by swirling gritty grus around inside the pit.

Look closely at the first image of this post, you can see the impacts of two climate regimes evident in the size and shape of the weathering pits as they have slowly formed under alternating climate conditions. Ice House Climate has dominated global climate regimes for the past 2.6 million years, the Pleistocene. At least four times during the Pleistocene, the climate has tipped toward continental glaciations, long periods of cold, damp weather. Glaciers did not reach Pahroc Pass, but Pleistocene glacial periods did cause great changes in the climate of the Southwest United States. During glacial periods, much more rainfall greened the playas and mountains of Nevada, the ocean of sagebrush was replaced by huge lakes, prairies, and forests. The larger diameters of the upper levels of the weathering pits pictured above formed during the wet glacial periods, the smaller, deeper inner pits develop more during the dryish climates like we enjoy today.

Weathering pits are extraordinary ecosystems of tiny organisms. Within minutes of moisture accumulating in a dry weathering pit, an ecosystem of micro life blooms: a food chain dominated by tiny shelled copapods is resurected with each rainfall that dampens dry pits. Adapted organisms go dormant with drying. Dormant life may last for decades until rainfall renews life.

Weathering pits are a resource of last resort for two reasons. First, pathogens may be present, left by passing animals or visiting birds, and second, these amazing tiny ecosystems should be left undisturbed unless water is urgently needed. Please conserve water in weathering pits by taking only what you need and by sterilizing what you take, away from the pit, not inside the pit. The oft-touted practice of sterilization by boiling in the pits using hot stones should be practiced only as a response to unintended life-threatening emergencies. Sterilizing pits is a thoughtless practice when used just for “practicing” outdoor survival skills.

It’s true, we suppose, that weathering pits are very unfriendly environments for pathogens that impact humans, but better safe than sorry. The weathering pits we found are on BLM lands used for open grazing. Cows carry pathogens. The boulders may prevent cows from approaching the pits, but not the birds that just left the cow patties below!

In the past, I may have tipped my dribbling canoe paddle blade high in the air and guided streams of dripping lake water past my parched lips to quench my thirst on big lakes; Boundary Waters & Quetico and Alaskan Lakes on the theory that way out there, the likelihood is low that I will ingest enough pathogens to become ill. Nevertheless, the risk remains. Outdoor Readiness suggests proper treatment of all wild water resources before consumption.

REI Inc., an outstanding major supplier of everything outdoor recreation is a great source for information rooted in authoritative resources, too. Follow the link for a detailed discussion of the use of wild water sources and concerns about purity of sources and pathogens found in backcountry resources.