lava
Eocene Wasatch: Pink Cliffs ROCKS IN BRYCE CANYON PARK
MESOZOIC
Cretaceous Undifferentiated: Gray Cliffs
sandstone
shale
coal
Jurassic
gypsum
Carmel limestone
Navajo sandstone: cross-bedded ROCKS IN ZION PARK
White Cliffs sandstone
Kayenta-Wingate
Triassic
Chinle: Vermilion shale,
Cliffs sandstone,
ash and
limestone
fossil wood
Shinarump conglomerate
Moenkopi: Belted shale
Cliffs
sandstone
oil RIM OF GRAND CANYON
Permian Kaibab limestone
In the development of the amazing variety of architectural features on
the canyon walls, the composition and structure of the Navajo formation
have served as controlling guides. In addition to the bedding
planes—horizontal, oblique, and curved surfaces—the Navajo has developed
parting planes (joints) that extend downward for short distances or pass
through the formation from top to bottom. These bedding planes and
joints determine the shape and size of the blocks that spall off from
the towering cliff walls. Unlike that of humid regions, this type of
erosion progresses from below upward; it causes the canyon to widen and
still retain its vertical walls.
[Illustration: (_Union Pacific Railroad photo_)
_The Sentinel viewed from the West Portal of the Mount Carmel Tunnel._]