The Elysium Fossae contain layers, also called strata.
Many places on Mars show rocks arranged in layers.
Sometimes the layers are of different colors.
Light-toned rocks on Mars have been associated with hydrated minerals like sulfates.
The Mars Rover Opportunity examined such layers close-up with several instruments.
Pictures taken from orbiting spacecraft show that some layers of rocks seem to break up into fine dust; consequently these rocks are probably composed of small particles.
Other layers break up into large boulders, so they are probably much harder.
 Basalt, a volcanic rock, is thought comprise the layers that form boulders.
Basalt has been identified on Mars in many places.
Instruments on orbiting spacecraft have detected clay (also called phyllosilicates) in some layers.
Scientists are excited about finding hydrated minerals such as sulfates and clays on Mars because they are usually formed in the presence of water.
 Places that contain clays and/or other hydrated minerals would be good places to look for evidence of life.


Rock can be formed into layers in a variety of ways.
Volcanoes, wind, or water can produce layers.
 Layers can be hardened by the action of groundwater.
 Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through.
 When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents.
Consequently, layers of dust could not later easily erode away since they were cemented together.
 
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The Elysium Fossae contain layers, also called strata. Many places on Mars show rocks arranged in layers. Sometimes the layers are of different colors. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates. The Mars Rover Opportunity examined such layers close-up with several instruments. Pictures taken from orbiting spacecraft show that some layers of rocks seem to break up into fine dust; consequently these rocks are probably composed of small particles. Other layers break up into large boulders, so they are probably much harder.  Basalt, a volcanic rock, is thought comprise the layers that form boulders. Basalt has been identified on Mars in many places. Instruments on orbiting spacecraft have detected clay (also called phyllosilicates) in some layers. Scientists are excited about finding hydrated minerals such as sulfates and clays on Mars because they are usually formed in the presence of water.  Places that contain clays and/or other hydrated minerals would be good places to look for evidence of life.

Rock can be formed into layers in a variety of ways. Volcanoes, wind, or water can produce layers.  Layers can be hardened by the action of groundwater.  Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through.  When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents. Consequently, layers of dust could not later easily erode away since they were cemented together.  
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Elysium quadrangle