| Geology: Oak Creek! |
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OAK CREEK CANYON CREATION: >30mya Area covered by rim gravel from mogollon highlands further south. Fault pushes EAST side UP, with the permian Kaibab limestone and Toroweap limestone eroded away, leaving the permian Coconino sandstone. 8-10mya The ancestral canyon erodes south, along the faultline, but not as deep as the present canyon. 6-8mya Volcanism, and at least five flows can be found erupting within and above the canyon. The final fifth flow is a cinder cone on top of Wilson Mountain. BOTH sides of the canyon are filled. WOW. 5mya The WEST side is uplifted, cutting Wilson Mountain with its bench on the east side of the fault (there's actually two fault lines here in-parallel). Oak Creek erodes into the most eastern of the faultlines. One thing you'll find curious is that the faultline cuts east, just north of Sedona, and then drops south behind Lee Mountain ('cat-woman' along SH179). Why did the creek leave the faultline? Airport Mesa is the ancient remains of the creek aluvium, so it's possible the creek slowly cut into its own aluvium, and finally 'locked' into its present position well west of the faultline. |
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I-17 INTERSTATE 17. This is whole area is covered in 'recent' volcanic lava flows overtop the permian kaibab limestone (from underneath a western-encroaching sea). The lava is so porous, that up on top of the rim, there are no year-round streams. Ancient spanish explorers noticed this, and called the local native-americans 'Sinaqua' or 'without water'. There are springs however ... near Kachina Village, Pumphouse spring was used for water for the steam trains in Flagstaff. The whole area is the largest stand of ponderosa pine in the world, stretching from eastern New Mexico to west of the San Francisco Peaks. ER EAST RIM. There are several good hiking trails that climb from SH89A up to the rim. Going north to south: Cookstone Trail (Pine Flat campground), Harding Springs Trail (Cave Springs campground), Thomas Point Trail (West Fork parking), Thompson Ladder Trail (up behind Indian Gardens area), and Casner Canyon trail (just north of Grasshopper Point). All are a bit steep, but fairly short and have really nice views. As you climb each, you move up the permian Coconino sandstone (white-yellowish), then move into kaibab limestone (white) near the top, and basalt flows on top. You'll also notice a change in vegatation, reflecting the limestone, and also reduced moisture near the top. Looking across to the other side, you'll see the highway switchbacks up north, permian layers across from you, and then Wilson Mountain toward the south, cut in half by the faultline. MB MIDGLEY BRIDGE. The bridge was built in the late 30s; before that, you drove up Wilson canyon a bit, and returned back. This is a great geologic 'stopover'. You're walking around on the permian Hermit shale. Looking upwards, you'll see the Schnebly Hill sandstone (also permian) that creates Ship Rock and most of the beautiful formations around Sedona. Higher up, the white permian Coconino sandstone is heavily cross-bedded, from winds from the north. Topping that is the permian kaibab limestone, which was the BOTTOM of a sea from the west. So, you can IMAGINE, you are well underneath the sea! Even worse, the layers ABOVE the kaibab were eroded AWAY, during the uplift of the Colorado plateau. Wow. Walking down to the bridge supports (be very careful), you move down into the Supai group, where you'll see limey portions of the Supai. The limestone is actually gray-white, but tinted red from the red rocks above. If you get a chance to visit Jerome, you'll find Redwall limestone high ABOVE you! ( but below the Supai here). In the Oak Creek below you, you'll see the large basalt rocks that broke off from the TOP of the whole sequence. More than 330m years (in theory of course)! OV OAK CREEK OVERVIEW. This is the best place to view the origin of Oak Creek Canyon. You're standing on the southern edge of the Colorado Plateau and the Mogollon Rim. If you look at the SH89A roadcut as it enters the canyon below, you'll see the black basalt that filled in the FIRST canyon. It originated about 6mi north from a fissure. This was AFTER the first fault pushed the east or left side UP with the Kaibab and Toroweap eroding away, and then being covered by multiple volcanic layers. A SECOND fault pushed the west or right side UP, which is why it is now higher. So, the canyon you see now is actually the SECOND time it eroded. If you look west down to the first turn in the switchbacks, you can see the actual faultline, which cuts further north back towards Flagstaff. As you drive down the switchbacks a little further, you'll see red dirt underneath the lava in the road cuts. This is the result of the tremendous heat from the lava. SH SCHNEBLY HILL ROAD. This dirt road leaves SH179 just east of the Oak Creek crossing in Sedona, and then wiggles its way up onto the rim and eventually I-17. The first couple of miles are driveable by everyone (bumpy), but the remainder is for high-clearance vehicles (closed in the winter). It follows the old Munds wagon trail up from Bear Wallow Canyon (yes, wallowing bears!), and has a nice hiking trail. You start out on the permian Hermit shale, and then slowly rise through the permian Schnebly Hill sandstone (from the eroded iron-rich ancestral rockies in Colorado). You'll eventually rise up to the kaibab limestone (end of the permian), and then top-out on basalt volcanic flows, that are much more recent. It's the sculptured red sandstone that catches your eye ... camel rock, merry-go-round, and the cowpies. There's a good overlook where you can see down Casner Canyon toward Wilson Mountain and its bench (see below). It's such a beautiful area all around, and for a true BONUS, you can watch the pink tourist jeeps ALL DAY LONG! SL SLIDE ROCK STATE PARK. This is a great park for kids, where you can slide down the permian Schnebly Hill sandstone. It appears just north of here on the west side of the highway. This used to be the Falls homestead, and thus you'll see orchard trees and farm buildings. On the northwest side up the creek, tunnels were blasted to bring water into the orchards. High up above you, you'll see the cross-bedded permian Coconino sandstone, which were desert sand dunes, with winds from the north. Want to see an 'arch'? (arches are eroded from behind; natural bridges are eroded from beneath). If you look south of Slide Rock park and mid-way up, you'll see an arch. It's quite beautiful. Boys used to roll old tires down it, from the top. Now those 'boys' complain about the visitors! SR SHIP ROCK or STEAMBOAT ROCK. This and all of the other formations around Sedona are Schnebly Hill sandstone, eroded from the ancient rocky mountains over in Colorado (not the present Rocky Mountains). Geologist can 'track' the erosion by measuring the 'grain' of the sand and also how rounded they are. The smaller the grain, the more distant the source. And a rough grain indicates recent deposition relative to erosion (a smoother grain indicates it 'bouncing' around for a while!). The red iron rust in the sandstone tends to 'seal' it together, thus providing much of the sculptured toughness and protection over the softer Hermit shale. None of these layers have much permian plant/animal remains, due to the dry sahara-like environment at the time. In the early days of Sedona, the wagon trail (Thompson trail) cut just 'under' Ship Rock, largely due to the difficult terrain near the creek, and frequent flooding. TL THOMPSON'S LADDER. This is actually a trail up to the rim on the northeast side of Oak Creek and Munds canyons. Park south of Creekside Mobile Village (which is south of the DQ). Then cross the creek. The trail leaves the floor of Munds canyon and may be hard to find. In the old days, it was the quick way up to Flagstaff for the Thompson family, who homesteaded the Indian Gardens area. Lumber was hauled down to build most of the early buildings here. The 'ladder' describes the extreme switchbacks! It's in this area that the basalt is deepest, reflecting ancient erosion along the faultline and subsequent volcanic eruptions (at least five). The view across to the west side and Wilson Mountain bench is just astounding. WB WILSON MOUNTAIN AND BENCH. If you stand on San Francisco peaks, you can see Wilson mountain to the south ... it's one of the most recognizable. On its top is the last volcanic eruption in the Oak Creek area. The 'bench' on its east flank is created by the faultline cutting across the volcanic flow. The whole sequence is more easily viewed from Schnebly Hill Road on the east side of the creek. If you're a hiker, the Wilson Mountain trail which leaves from the Midgley Bridge parking is very enjoyable and strenuous as well. WF WESTFORK. As you drive south on SH89A, many of the views are described in Wayne Ranney's 'Sedona Through Time', mile by mile. Buy it! West Fork is well known due to Zane Grey's 'Call of the Canyon', and has had several small resorts at its mouth. Now days it has trail parking and about a 3 mile trail up into West Fork canyon. The geology is all permian, and it's in this area that you begin to see the red Schnebly Hill sandstone. But its the permian Coconino sandstone above that is so amazing. It's heavily crossbedded, reflecting heavy winds from the north across deep sand dunes. If you look near the top, you'll see a 'green line' which represents the Toroweap limestone, and the Kaibab limestone on top. Both of these were from late permian seas from the west. The Toroweap is interesting, since it 'ends' in this area. Further west in Sycamore canyon, it's much thicker, and is also a different composition, representing just how near we are to the 'beach' area. The Toroweap generates considerable discussion among geologists regarding its classification (what else?). HIKING: The West Fork trail is interesting, but the Thomas Point trail nearby is MUCH more educational (and steep). It's a bit south of the parking area on the EAST side of SH89A. It's fun to climb the geological layers and then look across to the other uplifted side of the faultline. It's a quiet hike and really refreshing. |
| Copyright ©, 2007, dmbarnhart |
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