• 73,379 acres, 115 square mi
• 1929 - National Monument
• 1971 - National Park
• Southeastern Utah
• High Desert
Arches National Park
• 5 miles north of Moab
• Very close to 3 other parks
• Many other recreational opportunities
Arches National Park
• Environmental extremes
• Diverse collection of plants and animals
• Very delicate ecosystem
Arches National Park
• Paradox Basin
• Salt Valley
• Geologic Features
– Arches
– Balanced rocks
– Pillars
Arches National Park
• Colorado Plateau
• The Grand Staircase
• North of the Grand Canyon
• Mesozoic Rocks
• Terrestrial
Stratigraphy & Environments
• Wingate, Navajo, and Entrada Formations = layers of cross-bedded sandstone
• How do cross-beds form?
• Sands Dunes
• Triassic and Jurassic Sand Seas
• Climate?
Stratigraphy & Environments
• How do arches form?
• Entrada Formation - Dewey Bridge and Slickrock members
• Why are the fins and arches parallel to Salt Valley
• Joints
Question
• How is is possible to create a valley with only minor amounts of stream
erosion?
Salt Tectonics
• Deposition of evaporite beds in the Paradox basin
• Paradox Formation - Pennsyvanian (280 Ma)
– Gypsum, anhydrite, salt
Salt Tectonics
• Deposition of Permian and early Mesozoic rocks
• Density of rock > density of salt
• Salt flows - moves upward along faults and fractures
• Salt diapirs - salt walls (10,000 ft thick)
• Younger rocks thicken an thin between and over these
Salt Tectonics
• Laramide Orogeny
• Uplift and block faulting - Colorado Plateau
• 15 Ma - more uplift - followed by erosion
• Stream erosion and groundwater flow through rocks over salt walls
• Dissolution of salt
Salt Tectonics
• Salt dissolution - collapse of overlying rocks
• Salt valley
• Collapse and rollover
• Joints
– Parallel to valley
Fins and Arches
• Joints are the focus of weathering
– Water and frost wedging
• Exfoliation
• Sand blasting
• Arches form as lower part of fin weathers faster
• Entrada FM
– Dewey Bridge - shaley
– Slick Rock - indurated