GCT '09

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I remember how scientists raved when finding similar formations using the rovers Spirit and Opportunity on the surface of Mars. Known as hematite concretions - they formed perhaps 25 million years ago when minerals precipitated from groundwater flowing through much older Navajo sandstone, the spectacular red rock in southern Utah. They are also known by rock climbers in this region as "moqui marbles" as they give excellent grip in slick rock.