Several years ago I was working on a story about Strawberry Crater. I had already explored the dead volcano and had taken a number of photos but I had not captured one that showed the entire cinder cone from a distance. The problem had been the tall Ponderosa Pine trees that obstructed views around it.
Later on at home I used Google Earth to locate a minor, unnamed volcano off of Forest Service Road 546 that I thought might offer a clear view of the cinder cone. In February of 2015 I drove from Flagstaff and found the small volcano and hiked up to its rim. I was not disappointed, from the top I had a clear view of Strawberry Crater two miles to the north-east.
I took the photos I wanted then stopped to look around from my vantage point above the trees. O'Leary Peak was two miles to the south-west with Darton Dome next to it. I was slightly familiar with O'Leary, I had climbed it and the fire-tower at its top nearly 40 years ago. I didn't remember anything unusual about it at that time but now, from this direction, it looked very different. O'Leary Peak wasn't just next to Darton Dome but looked like it was inside of it.
|The Darton Dome / O'Leary sandwich.|
I had seen O'Leary Peak many times over the decades from Sunset Crater Volcano National Monument to the south and east but never from the north. From here it appeared as if O' Leary had bisected Darton Dome and shoved the two halves apart as it extruded up between the dome.
Technically Darton Dome only refers to the hill on the left, O'Leary Peak is the tallest one in the middle and an unnamed dome is on the right I'll call Dome B. When viewing O'Leary from the south or east Dome B is hidden from view.
Because of the cliff faces on both domes it appears they were once joined together.
Below is another photo of the cliff face on Dome B from a different angle. Some might argue it is the lateral edge of a thick dacite lava flow but I don't believe it would be that tall, vertical and void of vegetation. For the cliffs to have formed from stream erosion or glacial activity is unlikely. The O'Leary Mountain is just not big enough to provide the accumulation zone necessary for enough ice or water to erode those cliffs. It looks more like a sheer fracture to me.
|Dome B cliff face|
If I was a younger man and not handicapped I would climb up and get rock samples from each of the cliff faces and the flank of O'Leary Peak. Determining the rock chemistry and age of each flow might explain what happened here. O'Leary has been dated at 200,000 years old but I don't know about Darton Dome and Dome B. If they have the same chemistry and age that would suggest they were once joined. If O'Leary is younger than the domes then it erupted after the two domes were in place.
There in one more factor to add to this mystery that I only recently learned. Doney Fault is visible on the surface eleven miles to the northeast in the Wupatki National Monument. The north end of the fault heads away into the Little Colorado River Valley and the south end disappears under volcanoes and lava flows. If it continues on the same track under the lava flows it heads directly under Strawberry Crater and then O'Leary Peak.
|Google Earth Image|
|Google Earth Image|
That fault could have been the conduit for the Darton Dome eruption. After the dome cooled then motion on the fault could have fractured it and provided the conduit for O'Leary magma to reach the surface and leverage its way through.