"Moqui Marbles"

Most people, after exploring Zebra canyon, hike down Harris Wash to Tunnel canyon.  We, however, knew of an alternate route that was suggested to us by some friends.  This alternate route had a very surreal surprise that we were anxious to see.  The surprise was known as the "Moqui Marbles", large fields of little rocks scattered across the sandstone high up on the plateau in between Zebra and Tunnel canyons.  Rather than walking down the wash, we turned and hiked uphill to the plateau in between the two canyons.  Not long after reaching the top of the hill we started to see the marbles, at first just a few here and there, but soon we were finding large "fields" full of them.  There were so many scattered all around the plateau, there had to be literally millions of them.  

These were such an interesting geologic curiosity, I just had to do a little research to learn more about them.  It turns out that Moqui Marbles (according to the Science Daily website) are hematite concretions formed underground when minerals precipitated from flowing groundwater.  The marbles are very similar to rocks known as "blueberries" that have been found on Mars.  In Utah the rocks had iron in them originally.  Water travels through these rocks and leeches out the iron.  The water moves through cracks, holes, layers or pores until it reaches some place where the chemistry is different and causes the iron to precipitate out of the water as hematite.  After the concretions formed in groundwater, the surrounding Navajo sandstone slowly eroded away over millions of years, so the hard, erosion-resistant concretions accumulated on the ground.  

Seeing the marbles was certainly one of the highlights of our trip and the strangeness of seeing them would linger in our thoughts throughout the rest of the trip.  After getting our fill of seeing the marbles, we continued on our hike across the plateau towards Tunnel canyon.