Abstract
The mountains of the West are part of the American Cordillera in its widest part. They form the Laramide and Nevadan Belts and the Pacific Coast Ranges. I describe each of the major and many of the minor ranges, after a summary of continental-scale topography and its interactions with climate. These descriptions are brief overviews of the topics of Chapters 3–7, with variations based on which topics have the greatest importance. Glaciers and snow are much more dominant in the northern ranges: Cascade Range and the northern Rocky Mountains. Drought and water limitation are more important in the desert ranges and those with Mediterranean climates. I also sketch the human history of each. At the end of each chapter that follows, I revisit the ranges, with overviews of how each will experience the topic(s) of the chapter.
“Sometimes I do get to places just when God’s ready
to have somebody click the shutter.”
—Ansel Adams
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Notes
- 1.
I am greatly indebted to the many developers and authors of Wikipedia for general information in this chapter, such as the heights of peaks, names and numbers of mountain ranges, and geologic time scales of formation. I invite interested readers to delve further by searching Wikipedia for “North American Cordillera”, and go from there.
- 2.
The tropopause is the boundary between the troposphere (lower atmosphere) and the stratosphere (upper atmosphere). Its altitude varies from about 52,000 ft. at the Equator to about 30,000 ft. at the poles. Jet-stream winds, often above 150 mph, are typically felt near the summits of the highest Himalayan peaks (28,000+ ft.), making climbing impossible.
- 3.
The concentration of heaviest rain at middle elevations reflects two factors associated with increasing elevation: the decreasing moisture-holding capacity of the atmosphere and sparser obstacles to air movement (landforms). This has been observed most cleanly on volcanoes like Mt. Rainier, with its roughly conic shape allowing more and more air to pass unobstructed with higher altitude.
- 4.
The full quote is “K2: just the bare bones of a name, all rock and ice and storm and abyss. It makes no attempt to sound human. It is atoms and stars. It has the nakedness of the world before the first man—or of the cindered planet after the last”, about K2, the Earth’s second highest peak (28,251 ft.), in the Karakoram Himalaya, from Secret Tibet, by Fosco Maraini.
- 5.
The Pacific Ring of Fire has 452 volcanoes in all, 75% of the world total, and about 80% of the world’s largest earthquakes occur along it. Plate tectonics, driving the collision of lithospheric plates, are the cause. The Cascade Volcanic arc, including all U.S. volcanoes and three in southwestern British Columbia, was formed by collision of two plates in the Cascadia subduction zone, which is also a potential source of large-magnitude earthquakes in the Pacific Northwest, U.S.
- 6.
These numbers are from https://www.peakbagger.com/, and are based on a criterion that a peak is considered separate if it has at least 400 ft. of “clean prominence”, i.e., stands out from a ridge or massif sufficiently.
- 7.
A scalable map and other tools for displaying glaciers in the Western Mountains can be found at glaciers.geos.pdx.edu, courtesy of WMI scientist Andrew Fountain.
- 8.
Along a maritime-continental gradient in climate there are characteristic changes in both temperature and precipitation. In a continental climate, temperature has greater extremes, on both diurnal and annual time scales: days are warmer, nights are colder; summers are warmer, winters are colder. In a maritime climate, everything is wetter: more clouds, more rain, and more humidity, even on sunny days.
- 9.
Not predictably dry though. Many a prospective Cascade backpacker or cyclist, or Pacific Crest Trail traveler, has encountered up to a week of steady hard rain in August, often the driest month.
- 10.
The largest trees in the Pacific Northwest are found in the less than 5% of the original forests that remain after more than a century of logging. An inventory of the remaining giants is in Forest Giants of the Pacific Coast, by R. Schmid and R. van Pelt, 2002. Also see the website ascendingthegiants.com.
- 11.
Conifers vary widely in their vulnerability to cold, with those in cold climates having physiological adaptations to cold that have not evolved in species in more moderate climates. In general, though, needles are protected by a waxy coating, or cuticle, which shields them somewhat from cold (and also makes them generally less palatable to browsing animals). Some climates are so harsh than even this is not much of an advantage, and deciduous conifers (e.g., larches) are often dominant there.
- 12.
A popular measure of the density of forest cover is the “leaf-area index” (LAI), which estimates the average number of vertical layers of leaves in a forest canopy. This is different from canopy cover, though related. For example, a forest stand with 100% canopy cover, with a single horizontal layer of leaves, would have LAI = 1, as would a stand with 50% cover and exactly two layers. Forests in the Cascade Range can have LAI up to 9, the most in the West.
- 13.
And coming to a near stop in the 1980s with the conservation movement and associated legislation (see Chapter 9).
- 14.
The exact amount of remaining old-growth forest in the Pacific Northwest is debated, and estimates vary widely depending on the techniques used to make them. A good analysis of the estimates is in R.A. Norheim, 2001. How institutional cultures affect results: comparing two old-growth forest mapping projects. Cartographica 38:35–54.
- 15.
One legendary climber, Fred Beckey, almost single-handedly catalogued the climbing routes in the Cascade Range. His Cascade Alpine Guide, in three volumes, describes thousands of routes on hundreds of peaks (many of which saw Beckey on a first ascent), from scrambles to hard rock or ice, or both. Backcountry snowsports are equally challenging because of the variable (often bad) weather, complex terrain, and snow conditions that can be difficult to read for avalanche danger.
- 16.
Rock glaciers are what the name implies: moving mixes of rock and ice. They can be either frozen rock debris or ice glaciers covered by talus (fields of small-to-large boulders). A field study in 2008 identified 421 rock glaciers and periglacial rock-ice features in the Sierra Nevada, at elevations between 7300 and 12,900 ft. C.I. Millar and R.D. Westfall. 2008. Rock glaciers and related periglacial landforms in the Sierra Nevada, CA, USA; inventory, distribution and climatic relationships. Quaternary International 188:90–104.
- 17.
These can be the bane of backpackers and climbers, especially above treeline where there is little protection from lightning. Some notorious lightning traps are the granite domes in Yosemite National Park and elsewhere in the Sierra Nevada, where an unstable atmosphere can bring rapid changes in weather that catch travelers exposed and unprepared.
- 18.
Mammoth Mountain, though not volcanic, is a smaller version of Mt. Rainier in Washington in that it is a moisture trap for westerly winds. It is a haven for snow sports because it receives so much (fairly dry) snow and its northeastern exposures hold the snow often into mid-June.
- 19.
Water-balance deficit is commonly calculated as the difference between potential evapotranspiration (PET) and actual evapotranspiration (AET). Evapotranspiration is the combination of direct evaporation off the plant surface and transpiration (literally “water-crossing”), the movement of moisture through plant tissues. In a water-limited environment, plants adapt by shutting down or slowing metabolic processes that allow water to “escape” by evapotranspiration, such that AET is less than PET; the hotter and drier it is, the bigger the difference.
- 20.
Cold-air drainages (movement downslope of cold air, often at night) are an important microclimatic process that affects vegetation and snow cover directly, and modifies fire spread by changing the flammability of fuels (the vegetation, live or dead, that burns). Montane species whose normal elevational range is 1000–2000 ft. higher can be found in cold-air pockets at the lower ends of watersheds affected by them.
- 21.
Even without accounting for climate change, giant sequoia preservation is a delicate proposition. A major issue is that although the species is fire-tolerant, high-intensity wildfires such as have occurred early in the Twenty-first century can kill even mature trees. But total fire protection is not the answer either, because the giant-sequoia ecosystem is also dependent on low-intensity fires that thin the understory vegetation, particularly white fir, so that it does not become a ladder fuel (literally a step-ladder for flames to reach the canopy) that makes a fire intense enough to kill the sequoias.
- 22.
John Muir, Clarence King, and George Brewer are the best known early explorers of the Sierra Nevada high country. Norman Clyde is the best known from the early twentieth century, and is an analog to Fred Beckey (see Note 15) in the Cascade Range, though born 38 years earlier. Clyde has over 130 first ascents to his name, most of them in the Sierra Nevada.
- 23.
Fragmentation, and its opposite, connectivity, affect how organisms can move between locations and how physical processes such as snowmelt and streamflow may influence more distant locations. For example, wide valleys may be barriers to wind-dispersed seeds (especially upwind), but may not stop large animals such as grizzly bears, cougars, or lynx from dispersing between forest habitat patches unless the valleys are dense with roads or other built structures.
- 24.
I am glossing over a lot of detail here to accentuate the contrast between north and south. ENSO and the north Pacific surface dynamics (linked to another periodic phenomenon called the Pacific Decadal Oscillation) are themselves a teleconnection, although the cause-and-effect relationships are not fully established. To the extent that it affects the eastern Pacific Ocean, ENSO can have a strong influence on the climate of the Sierra Nevada and Cascade Range, and on the other Pacific Coast Ranges. Through ENSO’s effects on continental-scale westerly flows, there is a “dipole” effect on the West: in the north the El Niño phase of ENSO is associated with warm and dry weather, whereas in the south it is cool and wet. The reverse happens with the La Niña phase.
- 25.
T.F. Kittel et al., 2002. Climates of the Rocky Mountains: historical and future patterns, Chapter 2 in Rocky Mountain Futures, edited by J.S. Baron, ran an in-depth quantitative analysis of twentieth-century climate in the Rocky Mountains. I draw on their analysis for the summary here.
- 26.
There is some debate over whether there has been a systematic bias in recent measurements of high-elevation temperature, from the “SNOTEL” sites. Temperature sensors were switched at over 700 sites starting in the mid-1990s, and their calibration is in question. See J.W. Oyler et al., 2015. Artificial amplification of warming trends across the mountains of the western United States. Geophysical Research Letters 42:153–161.
- 27.
A working group for the Mountain Research Initiative (http://mri.scnatweb.ch/en/) identified five factors that could accelerate “elevation-dependent warming”: snow-albedo and surface feedbacks, water vapor changes and latent heat release, changes in surface water vapor and radiative flux, surface heat loss, and aerosols. (in Nature Climate Change 5:424–430).
- 28.
The named glaciers are a subset of “snow and ice bodies”, which may be just small patches of permanent snow that are indistinguishable from true glaciers when remotely sensed. In Colorado, there are many of these latter outside of Rocky Mountain National Park, but the lowest is still above 10,600 ft.
- 29.
The intense Waldo Canyon wildfire that burned 346 homes near Colorado Springs in 2012 was fueled by non-forest scrub vegetation, more than by these ponderosa pine stands. Not so the Black Forest Fire a year later, which burned 486 homes, all in an isolated patch of unusually dense ponderosa pine trees, east of the I-25 corridor but 1000 ft. higher.
- 30.
Until the 1990s, it was generally thought that the first migration to the Western Hemisphere was about 13,500 years BP, based on spear points at an archaeological site at Clovis, New Mexico. Since then, different theories have been proposed, including some based on genetic analyses that suggest that the first migration was much earlier (ca. 30,000 year BP). As I write, the issue appears to be still open.
- 31.
Of the 53 14ers in Colorado, two have roads to their summits, 14 have trails, and the rest are no harder than Class 4, which is fairly easy climbing but sometimes with significant exposure, where a fall could be fatal. “Bagging” all the 14ers is orders of magnitude easier than climbing all the 8000ers, at which only 43 people have succceeded (as of late 2019).
- 32.
See http://www.olympicrainshadow.com/olympicrainshadowmap.html for a map display of the effects of the rain shadow created by the Olympic Mountains.
- 33.
Lack of appreciation for the ecological consequences of this isolation led to the introduction of mountain goats to the Olympic Peninsula in the 1920s. Well-meaning people saw this as “natural” habitat for the goats, as well as the more mundane goal of providing fodder for hunters, but ignored the potential effects of goats on alpine plant communities not adapted to their presence. Goats have also become habituated to humans, and in 2010 a hiker was fatally gored. As I write, an effective and humane way to remove the over 300 goats now in Olympic National Park is still being sought.
- 34.
And in 1988, the US Congress designated 95% of the Park as wilderness. North Cascades National Park, in the Cascade Range, is also a “wilderness park”, with only half the acreage of Olympic National Park in the park proper, but much more connectivity with other wilderness landscapes.
- 35.
For example, see https://visibleearth.nasa.gov/images/87507/olympic-national-park.
- 36.
As recently as 100 million years ago, the Klamath Mountains may have been a continuation of the northern Sierra Nevada, but migrated west, as part of their complex geological history. Regional-scale geological structures match both those of the Sierra Nevada and the Blue Mountains of northeastern Oregon.
- 37.
This section draws heavily on J.K. Agee, Steward’s Fork. 2007, University of California Press. I refer interested readers to that book for details on many aspects of the Klamath Mountains.
- 38.
Pre-conquest fire regimes in the Klamath Mountains were a classic mixed-severity type, in which patches of complete mortality are interspersed with those of low-intensity surface fire and all intensity levels in between. These patches vary widely in area, creating the classic “complex mosaic” of vegetation in the aftermath of wildfire. Fire severity also varies among the many vegetation types, from redwood forest, to sparse woodlands and chaparral, to high-elevation (subalpine) forest.
- 39.
The packing ratio is a metric from fire-behavior analysis that measures the spacing of pieces of fuel within a specific volume. The optimal packing ratio for combustion is a density in between solid fuel (e.g., a big piece of wood) and sparse fuel (e.g., a few twigs separated by large gaps). The packing ratio of typical kindling is close to the optimum, hence its name and use.
- 40.
Technically, the highest peak in Nevada is Boundary Peak (13,147 ft.), but it is part of a massif whose highest point is Montgomery Peak (13,441 ft.) in California.
- 41.
One could of course argue that Great Basin National Park is also a sky island. We call it part of the Basin Ranges because of its location—far north of the sky islands of the Southwest—but most statements about the Southwest’s sky islands also apply to it.
- 42.
See the national parks websites http://www.nps.gov/grba/learn/nature/endemic-plants.htm and http://www.nps.gov/grba/learn/nature/endemic-animals.htm for the names of endemic plants and animals, respectively.
- 43.
If the San Francisco Peaks in northern Arizona are included, the highest is Humphreys Peak (12,633 ft.). With Great Basin National Park included, it is Wheeler Peak (13,065 ft.). The world’s highest sky island (depending once again on criteria used) may be Mt Kilimanjaro (19,341 ft.), with a prominence of 19,308 ft. (basically the entire mountain).
- 44.
As we have seen, the concept of a plant community can be slippery, and “lumpers” and “splitters” may arrive at very different counts. Nevertheless, several factors contribute to the exceptional diversity across distance in sky-island plant communities: the prominence of the ranges themselves, the accentuated lapse rates (changes in climatic variables with elevations) between these particular elevations (5000–11,000 ft.) in the Southwest, and the strong contrast in the effects of aspect (especially SW vs. NE) in these water-limited sites.
- 45.
A $1.5 billion telescope, the “Thirty Meter Telescope”, with eight times the optical power of any current optical telescope, is planned for completion in 2022 on the Hawai’ian volcano Mauna Kea. At 13,796 ft. asl (and equal prominence by standard definition), Mauna Kea is the ultimate sky island, which if measured from where it arises from the sea floor is higher than Mt Everest. Opponents argue that the observatory will be built on a cultural heritage site. As I write the conflict is unresolved.
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McKenzie, D. (2020). The Mountains. In: Mountains in the Greenhouse. Springer, Cham. https://doi.org/10.1007/978-3-030-42432-9_2
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