Land Lines
2:00 am
Thu December 15, 2011

Land Lines: El Capitan Doesn't Quite Fit the Mold

Every month this fall, KNAU has been taking you to places on the Colorado Plateau. They may be places you know, they may be places you've only heard of. It's a series we call Land Lines and today we're visiting Monument Valley. People come from all over the world to see this valley, one of the most evocative landscapes in the southwest. But at least one rock feature doesn't quite fit the mold of the mesas and buttes. In today's Land Lines, Rose Houk and Michael Collier explore the origins of El Capitan.

People come from all over the world to see Monument Valley--one of the most evocative landscapes in the Southwest. But at least one rock feature doesn’t quite fit the mold of the mesas and buttes. Rose Houk and Michael Collier explore the origins of El Capitan in today’s Land Lines.

"The roughness. The sharp edges. It’s almost like it’s telling you not to climb."

Something strange is going on here.  This is a land of flat rocks, but over my shoulder there’s a black spire holding up the sky.

Army scout Kit Carson gave it the name El Capitan, the southern gateway into Monument Valley.  Navajos call it Agathla.

"I’m Baje Whitethorn Senior, from the Reed Clan. In Navajo it would be Locah Dine. The place Agathla – where there’s plenty of wool. When I was a boy we used to go up there to help do the shearing to get the wool off the sheep.  [Singing]  That’s about riding a donkey and then all the lovely yarn flies in the wind.  [Singing]  To describe it, there’s really no words for it. But I’m an artist so I just portray it into colors. There’s so many. The deepest blue that you can create; the grays. It’s a dark image in the middle of some of the brightest reds and purples that you can imagine."

Monument Valley’s captivating forms haven’t always been here. Go way back, a couple hundred million years ago, when this valley was one continuous sheet of sedimentary rock. Rain fell and rivers rolled. The clawing fingers of erosion sought out cracks in the rock, and gradually sculpted the valley’s iconic buttes and mesas--Rain God, Elephant Butte, the Mittens, Totem Pole.

The architecture of Monument Valley owes its origin to the fact that some rocks are soft and others are hard. The mesas rest on pedestals of the Organ Rock Formation--a soft shale that retreats beneath the harder, overlying DeChelly sandstone. As the Organ Rock is undercut, entire slabs of sandstone fracture and fall. And over millions of years, the horizontal sedimentary layers are transformed into a vertical landscape. Broad mesas are worn into narrower buttes. Pencil-thin spires are the last left standing.

So what about El Capitan, that imposing 1,500-foot-tall spire?  It sure looks different.  Jagged instead of the classic slope-and-cliff profile of the others.  The reason: its volcanic heritage that began when magma violently erupted here about twenty-seven million years ago. The deep molten rock blasted a funnel-shaped opening all the way to the surface. After the initial explosion, shattered volcanic rocks fell back in on themselves. They cooled into a hard rock called minette, and fused into a plug more resistant than the sedimentary rocks. As wind and rain lowered the surrounding surface, the black rocks remained--the exposed neck of an old volcano. In fact, there are a number of other prominent examples in the neighborhood--like nearby Church Rock, and farther east, famous Ship Rock.

So the mesas and buttes of Monument Valley are mostly made of sedimentary rock, shaped by slow erosion, grain by grain. But El Capitan is entirely different--born of a catastrophic explosion of magma.

"It’s sort of like a silhouette that stays in your mind. I guess Agathla is overpowering."

I’m Michael Collier.  And I’m Rose Houk for KNAU Arizona Public Radio.