Sipapu Bridge EarthCache

This strenuous hike rewards the adventurous with a closer view of Sipapu Bridge. The first .6 miles of the trail contains two flights of stairs and one ladder. Then, for the next .6 miles the slope flattens and by hiking along a ledge you can get an excellent view of Sipapu Bridge. The last .6 miles contains steep switchbacks, exposed bare rock, handrails and two ladders. At the bottom you can stand beneath one of the world's largest natural bridges.

Sipapu Bridge is a natural bridge located in the Natural Bridges National Monument. The Bridge spans White Canyon. The span of Sipapu Natural Bridge was originally reported at 268 feet by Douglas in 1908, who also reported a height of 167 feet., ranking it as the fourth longest natural arch in the world. However, a measurement by Jay Wilbur and Craig Shelley in 2007 using modern methods (precision laser ranging and a mathematically precise defini-tion of "span") yielded a span of 225 ± 3 feet and a height of 144 ± 5 feet, demoting the arch to a seventh place ranking.

Based on specific criteria that separate natural arches from bridges, Sipapu is still ranked as the second longest natural bridge after the more famous Rainbow Bridge National Monu-ment, also in Utah.

This bridge, whose opening would almost house the dome of the United States Capitol, has taken thousands of years to form but will someday collapse and erode as part of the endless cycles of time and change.

The name of the arch comes from the Hopi word sipapu, a word for a symbolic portal from which the first human ancestors emerged.

Begin your hike at the interpretive sign at the top of the Sipapu Bridge hiking trail. As you hike down the trail keep your eyes open to answer the following questions.

The story started 270 – 260 million years ago during the early part of the Permian Period of geologic time. During the Permian Period, the west coast of North America ran approxi-mately north-south through central to western Utah. Sand grains that make up the sandstone were blown into the Natural Bridges area from the coast by onshore winds. At that time, wind-blown sand dunes were present in this area, and the region probably looked something like the modern Sahara Desert. The canyon that you see in front of you and the natural bridges that span the canyon probably formed within the last 10 million years, long after the sand grains were cemented together into solid rock.

Sand dunes continually move while they are forming. Although the grains of sand in the rock on which you are walking are now cemented together, at one time they were part of du-nes that actively migrated downwind. Cross-bedding is a sedimentary structure that results from the migration of dunes. Cross bedding forms when layers of rock are deposited at an-gles, rather than horizontally. In desert dune fields, cross-bedding is produced when sand grains blow up the back (or windward face) of a dune and are then deposited on the relatively protected front (or lee face) of a dune.

Since you walked the first steps you can see cross-bedding in rocks across the canyon; the nearly parallel lines in the rock that dip from left to right at about 20 degrees from the horizontal are cross-beds. The cross-bedding is actually a series of fossilized slip faces that formed on the lee side of a dune. High-angle cross-bedding, like that seen here, is typical in dunes that are deposited by wind-blown (rather than water-laid) sand. The direction in which the cross beds dip downward is the same as the direction in which the dunes migrated when they were active

(A) How many big white cross-beds you can count approximately in the first layer at the big cliff across the canyon?

Walk downhill till you reach the metal stairs. At the bases of the metal stairs look out ac-ross the canyon toward Sipapu Bridge. The stream in White Canyon once occupied the bot-tom of the canyon between you and the southeast buttress of the bridge. At that time a sand-stone wall existed beneath the present-day span of Sipapu Bridge .

(B) What happened, that the White Canyon stream broke through the wall?

Once the barrier was penetrated, the stream changed its course and straightened its channel by flowing through the wall. The old channel in front of you is now a cut-off meander, that is, a bend in the stream that is no longer used by the stream.

It is important to realize that the White Canyon stream never completely filled this can-yon.

(C) Instead, what do you think happened?

The first wooden ladder takes you down a steep part of the trail. Note that the wind-blown sandstone is much more resistant to weathering than the red silty sandstone.

(D) Why is the wind-blown sandstone behind the ladder much more resident to weathering than the red silty sandstone above you?

Looking out across the canyon, you can see dark stains formed by water seeping out of the rock. Note that the water tends to seep out preferentially where there are red silty sandstone layers..

(E) Why the water tends to seep out where there are red silty layers?

When the trail begins to level off, look down the trail. You see that the cliff protect the trees.

(F) What do you think how the cliff helps the trees?

Walk off the main trail to the bridge overlook. The ledge you are standing on formed where soft red silty sandstone eroded away above a hard cross-bedded sandstone. Look across White Canyon toward the north-northwest. Ancestral Puebloan ruins are present along a cliff about 50 feet above you.

Head down the trail toward the bridge. When you see a large boulder on the right side of the trail stop and look around. At this point you are at approximately the same elevation as the abandoned channel, the cutoff meander

From the top of the highest handrail you can look upward toward the mouth of the old channel. This gives you some idea of the difference in elevation between the modern channel and the abandoned channel.

Continue into White Canyon till you reach the last wooden ladder.

(G) How many steps has the last wooden ladder?

Now you stand beneath Sipapu Bridge. Feel free to take a picture and post the picture together with your logg.

Answer 4 Questions from A – F

AND answer Question G. This Question is a MUST!!!!!!

Send your answers to the following mail-adress:

Whenn all 5 answers are correct you can count this cache as a successful find.