WHERE IS THE OAK CREEK FAULT?

The Oak Creek Fault experienced earthquakes on November 25th, 2014 and again on May 5th, 2015.  The quakes were not very powerful, only magnitude 4.7 and 3.5.  Both occurred at night and they woke residents as windows rattled, picture frames fell off  walls and small rocks and trees tumbled down cliffs onto Highway 89A in Oak Creek Canyon.   Little damage was done but it raised awareness and was significant because the Oak Creek Fault has not been active in recorded history.  

After the quakes occurred I started to wonder where the Oak Creek Fault really is, other than the obvious, "Thru Oak Creek Canyon."  On geological maps and Google Earth it is only visible on the surface for 30 miles but it is certainly much longer than what can be seen.  Both ends of the fault are hidden beneath lava flows that have covered it up as it approaches the San Francisco Peaks at the north end, and Verde Valley at the south.  The fault has not moved in several million years or there would be obvious displacement on the lava flows that cover it, which there is not.

So where is the fault? 

Starting at the north end it comes from underneath the San Francisco Peaks, a large stratovolcano that dominates Flagstaff and Northern Arizona.  It then heads south and passes near or under the small mountain community of Baderville at Highway 180 near Snow Bowl Road. 

The fault line is in red.  It is hidden under the mountain and the

soil beneath Baderville so this is just a very approximate location.

 

The fault first appears at the south edge of Baderville where South Snow Bowl Road ends at a shallow canyon.  It then passes between A-1 Mountain and a small parasitic cinder cone next to it.  

  

Baderville at the base of San Francisco Mountain.

Baderville is build on loose sediments that are saturated with water. If the fault ever shakes long and hard the soil will liquefy causing foundations and homes to sink into the ground.

South Snow Bowl Road through Baderville.

From Baderville the fault passes east of A-1 Mountain and heads south towards the I-40 Interstate Highway.

The fault where it crosses Interstate Highway I-40.

Burlington Northern/Santa Fe railroad and the I-40 overpass.

Just south of the I-40 bridges the fault passes under the US Naval Observatory which is built atop a small cinder cone volcano directly over the fault.



The Naval Observatory is a military installation that takes

precise astronomical measurements for global navigation.

Immediately south of the observatory the fault makes its first appearance as Woody Ridge.  This is a 350 foot tall step in the earth caused by fault displacement that continues 10.5 miles to Oak Creek Canyon.  

   

The Flagstaff Arboretum complex lies 1.7 miles 

south of the observatory and next to the fault.  

 

Woody Mountain is another volcano next to the fault line.

   

It lies just 1/4 mile east of the fault. 

Flagstaff's botanical garden of native trees and  plants is also a rehabilitation center for injured birds.  

 

By the time Woody Ridge reaches Oak Creek Canyon it is 700 feet tall. 

At Fry Canyon, a mile north of Oak Creek Canyon, the fault splits into two branches. The platform between the branches is a suspended bench that broke away from the main fault and was left behind as the rest of the fault continued to rise.  Forest Service Road 535 climbs the bench which is a popular camping area in the summer months for large parties and overflow campers from Oak Creek Canyon.

Oak Creek Fault splits and passes to the right and left of the suspended bench.

  

Both branches (1 & 2) of the fault continue on into Oak Creek Canyon where they cross Highway 89A at the Switchbacks. There are eight locations where the two fault lines cross under the highway. Only two (3 & 4) are readily visible. In addition, there are several slump blocks on the steep slope but I show only one (5) that can be easily seen. These are fractured blocks of earth that are slowly slipping down into the canyon.



1.  Oak Creek Fault - the main fault.

2.  Secondary fault branch.

3.  Location where the photo below was taken.

4.  Location where the photo below was taken.

5.  Location of the slump block fracture - photo below.

6.  Viewpoint - elevation 6390' - photo below.

7.  Pumphouse Wash - elevation 5700'.

8.  Oak Creek Canyon and Oak Creek.

9.  Sterling Canyon.



Photo point 3:  The Oak Creek Fault.

On both sides of the fault the rock has been pulverized and a fault zone a hundred feed wide is easily eroded.  On January 23, 2010 record rains and snowfall scoured this gouge into the fault zone.  It may eventually undermine the highway above it.  ADOT will need to deal with it at some point.

Photo point 4:  Oak Creek Fault. 

Heavy rains also enlarged this scar into the crushed sandstone. 

Photo point 5:  A slump block fracture.

Two more slump block fractures.

Photo point 6:  Geology board at the Oak Creek Canyon view point.

Photo point 6:  Oak Creek Canyon from the viewpoint.

1.  The main fault line.

2.  The secondary fault branch.

3.  Pine Flat Campground.

Below the switchbacks water flows out of the ground at both faults.  Sterling Springs, the headwaters of Oak Creek, gushes out of the main fault. Harding Spring, the artisan well next to the highway, flows out of the secondary fault.  There are also several ambiguous springs located in the creek bed itself.

At Pine Flat Campground the two faults converge.  Oak Creek and Highway 89A meander over the fault as they travel down the canyon.  At Slide Rock Lodge the fault splits again, one branch staying with the creek and the other veering for Wilson Mountain.

A secondary branch slices the side off Wilson Mountain and splits a volcano in half creating the suspended block known as First Bench.  There are hiking trails to First Bench and the top of Wilson Mountain from Ensinoso Picnic Grounds and Midgley Bridge.

The core of the volcano has been laid open by the fault.

   

1.  The volcano erupted through the Kaibab Limestone Formation after it had risen above sea level.  

2.  A dense magma conduit that likely fed the volcano.

3.  Layers of reddish volcanic cinders known as tephra.

4.  Older lava flows that were lifted and tilted by this volcanoes eruption.

Just south of  the Rainbow Trout Farm the main fault exits Oak Creek Canyon altogether and heads up Casner Canyon to Schnebly Hill directly east of Sedona.

The last mile to the top of Schnebly Hill. 

Fault escarpment 

The fault escarpment is a pulverized zone of Coconino Sandstone exactly like what is found on the Switchbacks.  Schenbly Hill Road was dug into the side of it.

The fault is buried under a talus slope and covered

with vegetation across the face of Schnebly Hill. 

It passes through the saddle between Schnebly Hill

and Munds Mountain and into Jack's Canyon beyond. 

Jacks Canyon makes a right turn at the far end 

and leads 3.5 miles to The Village of Oak Creek.

After the Oak Creek Fault crosses into Woods Canyon (Dry Beaver Creek) it is buried under thick lava flows 4 to 16 million years old.  I don't believe it just stopped there because Lee Mountain is still 400 feet higher than the lava flows on the opposite side of Jack's Canyon.  The fault may continue and cross Interstate Highway I-17 south of the Stoneman Lake Exit and into Rarick Canyon or just peter out altogether.  There are no surface indications to what takes place.

Oak Creek Fault is a normal fault, meaning that the opposing sides move vertically.  Because of his it doesn't necessary have to travel in a straight line and can wander along changing planes of weakness.  In comparison, the San Andreas Fault slides horizontally and for hundreds of miles is basically a straight line. 

There are at least five volcanoes that are on or next to the Oak Creek Fault:  the San Francisco Peaks, A1 Mountain, Naval Observatory Hill, Woody Mountain and the Wilson Mountain volcano.  This is because deep rooted faults can provide a conduit for magma to reach the surface.  Oak Creek Fault is continuous into the basement granite rocks of the North American Continent.



This essay is not a prediction of future movement or volcanic activity, only where the fault is located.  Neither the Oak Creek Fault or any of the slump blocks on the Switchbacks have shifted in recorded history nor did they slide during the recent earthquakes.  Conclusions about the Oak Creek Fault are based on my research and observation of the rock  strata.  I believe the data I have presented here to be accurate; however, what I have presented here is solely my opinion.