In the late Miocene era 6 million years ago, our region underwent uplifting, and the Colorado River drainage system was cut through miles of strata, exposing the Navajo sandstone.

As erosion uncovered the formation, light hydrocarbons like methane gas may have been released from the rock, flooding into the atmosphere. As it flowed out, it bleached the sandstone, at times leaving streaks that show the flow patterns.

Chemical experiments have shown hydrocarbons can bleach sandstone.

"We're still looking for the smoking gun that would prove this happened," Beitler said, "unequivocal proof that it was hydrocarbons instead of something else."

They also would like more evidence about the rate at which the sandstone was exposed.

At places where the Navajo sandstone remains buried, "it's still full of gas and hydrocarbon," she said. The Overthrust Belt of the Utah-Wyoming border is a big natural gas field. Tar sand resources are found elsewhere in the region.

In southern Utah, where the Navajo sandstone is exposed, higher layers are bleached or retain red bands within the lighter rock.

The scientists used Landsat photos to map the extent of the bleaching of the southern Utah sandstone. They made checks on the ground at locations like the San Rafel Swell and the Circle Cliffs to verify the colors, finding the satellite images were "excellent" indicators.

The hydrocarbon reservoir must have been immense, they found. They studied flow patterns and estimated volumes of material released.

Their map led them to conclude "release of methane contained in the Colorado Plateau Navajo reservoirs, if rapid enough, possibly introduced enough carbon into the atmosphere to drive climatic warming."

In the same period, Earth was undergoing a warming period, the last time it was hot before the ice ages.

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