Sequoia National Park

As our journey through the Sierra Nevada continues, we will now explore Sequoia National Park, the home of the world's largest trees by volume. These organisms, known as giant sequoias, occur naturally only in groves on the western slopes of the Sierra Nevada. They thrive in this environment, particularly between 5,000 and 7,000 feet in elevation, due to its humid climate which is characterized by dry summers and snowy winters. The soil composition most conducive to giant sequoia growth is granitic-based alluvial soil. Alluvial means that the granitic rock of the Sierra Nevada is weathered into a fine-grained soil, rich in minerals, and then deposited by water flowing over flood plains or in river beds. Thus, the giant sequoia groves are almost always located in deep, well-drained sandy soil with an average pH of 6.5 (slightly acidic).

Depicted above is a giant sequoia known as the General Sherman Tree. By volume, it is the largest known living single stem tree on the planet. However, the General Sherman Tree is not the tallest tree on Earth; at 396 feet, that is a distinction which belongs to the Hyperion Tree, a Coast redwood. General Sherman is not the widest tree on Earth; both the largest cypress and largest baobab have a greater diameter. Nor is the General Sherman the oldest known living tree on Earth; the Prometheus tree, a Great Basin bristlecone pine, holds that distinction at approximately 5,000-years-old. But with a height of 275 feet, a diameter of 25 feet, an estimated bole volume of 52,513 cubic feet, and an estimated age of 2,300-2,700 years, it is among the tallest, widest, and longest-lived trees on planet Earth. 

Another incredible aspect of Sequoia National Park is its intricate cave systems. There are at least 240 known caves in the park, many with endemic cave fauna; the most impressive of these caves is Crystal Cave. Crystal Cave has formed within marble of the Sequoia Pendant, one of many metamorphic pendants trending northwest across the Sierra Nevada. A pendant is the downward extension of the surrounding rock that protrudes into the upper surface of an igneous intrusive body; in this case, the intrusive body is the granitic batholith which comprises the Sierra Nevada. The Sequoia Pendant is approximately 16.7 miles long and 1.24 miles wide. Crystal Cave has formed in a narrow lens of coarsely crystalline, vertically bedded marble. Most passages in Crystal Cave have developed on strike, parallel to the axis of the marble lens and the metamorphic pendant. Many of the cave walls are composed of schist, a medium-grade metamorphic rock. With its ornate marble polished by subterranean streams and decorated with stalactites and stalagmites, Crystal Cave is a natural treasure to behold.

This picture shows the incredible stalactite formations in Crystal Cave. The cave is located on the western slope of the Sierra Nevada in Sequoia National Park. The Sierra Nevada is a unique location for the formation of caves. Below the glacially sculpted range crest, the broad western slope of the range descends in a series of undulating low relief upland surfaces punctuated by deeply incised river canyons. The vast majority of caves in the area have formed in proximity to these rivers. Additionally, the climate of the Sierra Nevada is distinctly Mediterranean, with cool, wet winters and hot, dry summers. As a result, groundwater recharge for the caves of the Sierra Nevada is usually allogenic, meaning it is derived from sinking streams that originate in granitic catchments. These areas of drainage are often steep, dropping several thousand meters over very short (6.2-18.6 miles) distances. Snowfall in the winter provides much of the precipitation in the southern Sierra Nevada. Temperatures increase rapidly in the springtime which results in a dramatic seasonal run-off with stream discharges rising two or even three orders of magnitude over the course of only a few days to weeks. Although it is less frequent, much larger floods can occur due to unseasonably warm rainfall onto a dense snow pack. Recent events of this nature have occurred within the study area in 1957, 1969, 1997 and 2002. Because of the steep granitic catchments that supply water to the caves of the Sierra Nevada, and the dominance of sinking stream recharge and flooding, sediment flux through cave passages is high, complicating cave conduit development.

Crystal Cave and adjacent small satellite caves are situated at elevations ranging from 4,547 feet to  4774 feet, and occupy the lower 210 feet of a marble ridge approximately 525 feet long and 131 feet wide. Contained within this narrow ridge, there are 3 miles of surveyed cave passages. A high percentage of voids within the bedrock, approximately 11%, have been produced as a result of the extensive cave passages and the small size of the marble lens. The cave and ridge are located between Yucca and Cascade creeks, two tributaries of the North Fork of the Kaweah River. These streams have incised as much as 820 feet into the surrounding bedrock in the vicinity of Crystal Cave, forming deep canyons with steep (up to 55°) hillslopes. Although they are located near the western limit of Pleistocene glaciation, these drainages have remained free of ice during periods of glaciation, so their rugged relief is solely a product of stream incision.

Figure A: This map represents the location of Crystal Cave in the southern Sierra Nevada.
Figure B: Plan view of the cave showing passage layout, hydrology, and geology. Satellite caves shown in dark gray; streams shown by light gray lines, dashed where intermittent or inferred.
Image courtesy of: http://www.caves.org/pub/journal/PDF/V67/v67n2-Despain.pdf

This is a profile view of Crystal Cave and surrounding caves showing pronounced cave levels. The highest level cave, Bear Den, formed first, while the lowest level cave, Entrance Passage, contains an active vadose stream and several shallow phreatic pools. A vadose system is water that is located in the zone of aeration in the earth's crust above the ground water level, while phraetic pools result directly from the groundwater. 

Six distinct levels constitute the Crystal Cave system (the term “level” here refers to a specific phase of cave development and does not imply a lack of passage gradient). The vertical relief of these levels is 210 feet. The largest passages in the cave are contained within four of the levels; these are primarily large, low gradient tubes and wide canyons. The other two levels have smaller, shorter passages with more prominent vadose incision in passage floors. All but one of the levels are connected by steep, narrow, meandering vadose canyons. The highest levels of the cave are located near the eastern, upstream edge of the marble; the subsequent lower levels exhibit a progressive shift of cave development toward the western, downstream edge of the marble. A perennial stream can be found at the lowest level of the cave. An extensive breakdown collapse is superimposed upon previously intact passages in the northern upstream portion of the cave. This collapsed area extends from base-level pools in the lowest sections of Crystal Cave to the overlying hillslope. Included among these collapsed areas are the Dusty Breakdown Cave and the northernmost 213 feet of Crystal Cave, north of the Fault Room.
Image courtesy of: http://www.caves.org/pub/journal/PDF/V67/v67n2-Despain.pdf

Works Cited

Allen, Casey. Professor Allen's Geog 1202 Syllabus. University of Colorado Denver, 2013

Despain, Joel D., and Greg M. Stock. “Geomorphic History of Crystal Cave, Southern Sierra Nevada, California.” Journal of Cave and Karts Studies, v. 67, no. 2, p. 92-102.

NPR. "The World's Tallest Tree is Hiding Somewhere in California." National Public Radio, 08 April, 2011. Accessed 14 April 2013.

NPS. "The General Sherman Tree." National Park Service. Last Updated 23 April 2013. Accessed 14 April 2013.

UANews. "Keepers of the Prometheus: The World's Oldest Tree." University of Arizona, 23 January 2013. Accessed 14 April 2013.

Perhaps one of the most mystifying sights in Sequoia National Park is this great sequoia growing around a boulder. If the boulder appears to be out of place to you, that's because it is. In fact, this boulder is a glacial erratic, meaning that it was carried to this location over dozens of miles by a glacier.

An awe-inspiring view of a giant sequoia grove. The sequoia in the middle of the photograph demonstrates that the soil in which it is growing has been moving down slope in a mass wasting process known as creep. Creep is the slow downhill movement of soil and regolith. The top layer of soil was likely moving faster than the soil beneath, causing the young sequoia to bend down slope. As the roots stabilized the soil, the process of creep was greatly diminished and the sequoia was then able to grow straight.