218 
NATURAL BRIDGES OF UTAH 
reaches the headwaters of what farther down is a mighty chasm. 
Almost immediately after the canyon is entered it becomes so deep 
that the level country, into which it is carved, is lost to view, and 
the traveller’s vision is limited by the steep walls of the meandering 
defile. Occasionally the trail leads directly along the channel 
of the intermittent stream, and at other times it climbs to the 
flanking cliflFs in order to avoid waterfalls or other obstructions. 
Six or eight miles below the point where the trail first enters 
the canyon, the great Edwin bridge is situated. This is in Arm¬ 
strong canyon. The Carolyn bridge is four miles below the 
Edwin bridge and immediately at the junction of Armstrong and 
White canyons. From here the Augusta bridge is situated two 
miles up White Canyon. It will thus be seen that the three 
bridges occupy the apices of a triangle of two to four miles 
on the side. 
As incidentally pointed out in a preceding paragraph, the rock 
formations of this particular area consist essentially of light- 
colored Triassic sandstones. It is more clearly accurate, however, 
to describe them as buff and light-red in color rather than as 
white or whitish, except perhaps as seen from a distance. The 
upper one to two hundred feet are characterized by pronounced 
cross-bedding, much like that of the Jurassic sandstones farther 
to the north and west. Immediately beneath this member is an 
unusually massive sandstone free from interbedding and frac¬ 
tures. Next below is a thin stratum, 4 to 8 feet thick, of easily 
weathered argillaceous sandstone. This in turn is followed by 
another massive member which continues to the bottom of the 
canyon. 
The origin of the bridges is, of course, intimately related to 
the geological formations in which they occur, and, in consequence, 
the essential structural features should be kept clearly in mind. 
In this immediate connection by far the most important members 
are the two massive sandstones and the intercalated weak clayey 
layer. All of these formations occur in the lower depths of the 
canyons and are virtually identical at all of the three bridges 
mentioned. 
All of the streams in this region are deeply entrenched and 
most of them are very crooked. Although all of the bridges 
owe their origin to stream-mandering, yet none of them has arisen 
