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EarthCache

Whitewater Canyon Overlook

A cache by Blue Grass Tom
Hidden : 11/19/2008
In Iowa, United States
Difficulty:
1 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Watch the cliff edge, and wear blaze orange during hunting seasons here. There are wide, level mowed lanes of prairie on your way to an overlook, and winding challenging terrain down to the creek.

The word “canyon” is rare among Iowa place names. But there it is, with a creek flowing from southern Dubuque County into northeastern Jones County, its valley abruptly narrowing to a constricted gorge bound by steep bedrock bluffs, a series of sharp turns and tight meander loops deeply entrenched into the surrounding landscape: Whitewater Canyon. Water and time created this naturally beautiful site through the process of erosion. The zig-zag course takes nearly three miles to cover a two-mile, straight-line distance. Below the canyon, the creek valley broadens again before emptying into the North Fork of the Maquoketa River.
Looking out across the rolling countryside from Highway 151 or county roads, you could miss this canyon all together. Only on near-approach does the sudden, 150-foot drop into this geological gem come into full, spectacular view.
In addition to great scenery, this canyon offers lessons in Iowa geology!

Such eye-catching features in Iowa’s scenery are usually the result of underlying geological conditions. The landscape-changing factor in this case is bedrock: durable dolomite—a magnesium-rich limestone.
This rock formation, which lies much deeper under central and southwest Iowa, was deposited as limey mud and shell fragments in a warm, clear, shallow sea that covered the interior of North America about 430 million years ago (Silurian age). In fact, the exposed bedrock contains many marine fossils.
Though this bedrock is most exposed in the canyon itself, you can catch glimpses of it nearby: in weathered rock knobs poking through to the land surface, in layered strata exposed along road cuts and in local stone quarries. The usual mantle of glacial-age clays and silts that masks Iowa’s bedrock elsewhere across the state is quite thin here. Upstream, Whitewater Creek and its tributaries have occasional brief contacts with bedrock, but nowhere more dramatically than in beautifully carved Whitewater Canyon.

Looking into the canyon from blufftop overlooks, one’s eye is drawn to its straight, sheer walls of rock and to the winding course of both creek and valley below.
The bold bluffs actually follow fractures, or planes of weakness, through the bedrock. These developed earlier in the region’s geologic history when rigid bedrock masses fractured under long-term stress associated with regional warping of the Earth’s crust. The resulting vertical fractures, called “joints,” tend to occur in parallel sets and at nearly right angles to each other.
Whitewater Creek, taking the path of least resistance through the dolomite, follows first one fracture trace and then another, often with right-angle turns. This erosion pattern is repeated in deep vertical crevices that open behind and parallel to major cliff faces, in tributary ravines entering the canyon at nearly right angles, in rectangular bedrock “chimneys” standing apart along the bluffs, and in angular blocks of bedrock lodged on the canyon’s lower slopes. State preserves and parks—such as White Pine Hollow, Backbone, Maquoketa Caves and Palisades-Kepler—are other places where Silurian bedrock produces dramatic effects on both topography and drainage patterns.
In addition to these pronounced vertical features, visitors will notice prominent horizontal ledges, overhangs and recesses. These occur along “bedding planes” that reflect the sedimentary rock’s original accumulation on an ancient sea floor. These layers, accentuated by differences in their resistance to erosion, provide picturesque relief to the rock faces as well as convenient footholds for vegetation.

Now, a word about "dry prairies." At the lowest end of the moisture spectrum, dry prairies are dominated by short- to mid-height (up to 2 feet tall) grasses and forbs (flowering plants) adapted to dry conditions. Little bluestem, side-oats grama, and porcupine grasses typically dominate; dotted blazing star, pasque flower, and puccoons are characteristic forbs. Biologists identify four subtypes of dry prairie.

The sparsely vegetated barrens subtype occurs on deep deposits of sand left primarily by glacial meltwater rivers. Winds have often reworked these deposits into dunes during subsequent periods of severe drought.

The sand-gravel subtype occurs on nearly level to steeply sloping gravel-rich deposits left by melting glaciers or deposited along the shores of large glacial lakes.

The hill subtype, richest in species, climbs steep slopes of loamy till also deposited by glaciers.

Along steep Mississippi River bluffs in southeastern Minnesota and northeastern Iowa, the bedrock bluff subtype, often called goat prairie, sprouts from a thin layer of soil over bedrock.

Email these answers to me for credit for this cache:

1) Whitewater Canyon was formed by what basic process?
2) To your right at Ground Zero is a rocky area with prairie grass and plants on it. Which of the 4 dry prairie subtypes is this?
3) See the creek bend to the left in front of you - from the reading above, what would you say is the cause of the bend?

A picture is not required but please add one or more, so that we can enjoy the beauty of this spot during various seasons! Have fun!

(Note: The factual data here is drawn from articles by Iowa and Minnesota DNR personnel in various articles.)

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Current Time:
Last Updated: on 11/9/2014 5:29:01 PM (UTC-08:00) Pacific Time (US & Canada) (1:29 AM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum