H18: Fossil Canyon: Hurricane Cliffs, La Verkin, Hiway 9 01/18/06

H18: Fossil Canyon: Hurricane Cliffs, La Verkin, Hiway 9 - S24 T41S R13W (1/18/06)

Fossil Canyon: Hurricane Cliffs, Laverkin (1/18/06), Hiway 9

S24 T41S R13W has a trail climbing to the east above a fossil canyon in the Permian Kaibab (Pk and deeper). This is shown to be a fossil canyon, belonging to a previous uplift of the Hurricane fault. A fossil canyon once channelled water into an older drainage, but no longer is part of the existing drainage. This author perceives the canyon to be fossilized by virtue of the fact that there is no canyon on the farmlands below, and the canyon disappears at about the 3320 foot elevation (although it is a 200 foot deep canyon at higher elevations).

Pk tops at 3800, indicating that there was total uplift of about 500 feet (150 m.) in previous uplifts. Such an elevation may represent more than one uplift in the Pliocene and earlier.

The canyon is ragged, but displays a trend almost NW-SE, perpendicular to the Pine Valley Mountains (almost perpendicular to the Virgin anticline), but the dominant factures exposed in the mouth of the canyon are NE-SW.

This hints that the fractures belong to the previous Pliocene epoch, and not to the present stress system running N-S. The author believes that the dominant stress system has changed from NW-SE in the Pliocene to N-S now, via analyzed fractures in the Plv (Pliocene Verde Formation, near Sedona, AZ).

Virgin river right-angle turns, at 1-2 miles south of this fossil canyon, are parallel to this orientation of 300-120 degree orientation (except for orthogonals, running 120-30 degrees from north). The author believes that the stress system changes at the Hurricane fault, from the one just listed to one running N-S in quaternary times. This is a major factor exhibited, which will allow some understanding of the mechanism of the uplift causing the fault. The thicker crust to the east (versus thinner in the transition and B&R zones to the west), the unusual heat flow westward (shown by the St.G. geothermal field and volcanoes near the fault), and the un-distorted Colorado Plateau (versus major distortions shown in the stratigraphy to the west) all are clues to the mechanism of uplift of CP.

A factor not yet understood is that of wrenching of the CP just to the east of the great fault (as shown by continuous broken blocks, in two dimensions, of Pk near the Virgin River). Fissures near the river hint that the opening of the canyon for drainage of the Virgin through highlands nearby was preceded by significant fractures in the stratigraphic column, allowing the river to flow westward over the raised rim of the scarp. This fissuring and fracturing is still proceeding, as evidenced by the linear breaks (both parallel and diagonal to the 800 foot deep Virgin canyon) in the highlands hiked last week.

Upon trekking the same trail above the major canyon a second time, all the way to the top of Kb, additional facts are presented below:

1. The latest scarp (N-S Hurricane fault) is first seen at the base of the uplift, although there are talus and debris in the subtle foothills at the initial climb from below. This scarp confirms that there is not a significant canyon below 3300 feet elevation, while a 200 foot canyon, washed by ancient streams, is shown above. The drainage area, as seen on top of the plateau, is from the Hurricane Mesa, but still delivers occasional precipitation. There is evidence of occasional trickling of rainfall, forming a foot-deep gully below 3300 feet (but not on the flat farmlands). Whatever gully formed at the mouth of the previous creek is now covered by soil, with no evidence of erosion below. This indicates that after sinking of the farmlands (relative to rising of the scarp) there has been only deposition, and no significant canyon-forming erosion with the last uplift. The conclusion is that there was no through-flowing creek in the present cycle, and that there was a measurable scarp left over from the previous uplifts (before the last one). This is not the same circumstance noted for the stream just north of North Creek (north of Virgin Town), where Pine Valley intrusives were found- indicating that there was no scarp between that location and the PV Mountains at the 1-3 million year age. This indicates that at least two uplifts have occurred since the 1 m.y. time (the ones noted at the fossil canyon;

2. There are 90 degree turns in the fossil canyon indicating that major fractures were instrumental in creating this local stream channel, in Pleistocene time. Remembering that the Pleistocene had considerable more precipitation than now, this indicates that the present uplift is mainly younger than the Recent (14,000 years and less), because of the obvious lack of erosion by rainfall in the youngest foothills. We have calculated that the uplift at Honeymoon canyon at the AZ border, to have occurred at .8 m.y. (<1 mm/year) This would have included a major part of the ice-age, where there would have been significant more rainfall. If at Laverkin, the uplift started after the major rainfall (making little erosion, in the farmland), then the meter elevation difference between fault and farmland would calculate an uplift rate of 50,000 mm/14,000 years, or about 3mm/year. This is significantly different from that calculated by me or others in other locations;

3. There were no rounded stream gravels anywhere in the upper reaches of the fossil canyon, indicating that the erosion is entirely from recent breakage of the Kb and red cliffs in the Hurricane Mesa nearby. Only angular limestone and sandstone pebbles were found. A stock tank was constructed in the streambed, to leave diggings with the same pebbles. There is no evidence of a through-flowing stream or of capture of the previous stream by the present Virgin River;

4. This fossil canyon is anomalous, compared to all other evidence of uplift east of the Hurricane Fault, hinting that the local area cannot be compared directly to the Hurricane fault south of the airport towards the Grand Canyon. The next southerly 50 miles of the fault and cliffs- scarp seem regular and consistent (same amount of uplift and retreat of the Colorado Plateau), compared to this part near the Virgin River; and

5. There must be a local stress concentration, such as a wrenching, rotating of the crust, or other major fracturing, in the Virgin River- Hurricane scarp area to have allowed the Virgin to escape through the elevated rim. This is strongly indicated by the unusual concentration of volcanic vents, by the young deformation (post Laramide) of Mesozoic sedimentary rocks, by the un-filled fissures and trenches near the Virgin, and by the large up-to-the-west dip of Kb in the Toquerville area.

Kinetics of Colorado Plateau Transition- Hurricane fault

1. The latest uplift of the CP is Pleistocene, possibly Pliocene in age (1-3 million years); this does not include the uplift created by the Laramide, or Intrusions such as the Pine Valley Mountains. This age is estimated by the basalt (greater than 1 m.y. age) covered mesa between Dalton and North Creeks, northwest of the town of Virgin, where PV boulders have been carried by river flow across what is now a scarp between PV and the CP;

2. During the Pleistocene, at least three episodes of uplift have occurred, as seen by the terraces and stages of erosion at and above the Hurricane fault;

3. The uplift is continuing, with an estimated movement of <1 mm./year, as calculated by the retreat ("walking") of the scarp at the AZ border, of about 1300 feet from the vertical beds to the present scarp, using a retreat rate calculated from the Permian of the Mogollon Rim near Sedona of 600 years/foot;

4. The uplift left scarps in previous cycles, as evidenced by the 200 foot canyon in S19, east of Laverkin, with a scarp below- where there is not an alluvial fan or even a well-developed outwash plain. There is deposition, showing that if there was a canyon left from the previous uplift, there is only flat farmland now;

5. The uplift is exaggerated near the Toquerville- Hurricane towns, with cross-faulting and rates >1 mm/year;

6. There is a rotation of the stratigraphic column near the Virgin River and the Hurricane cliffs, as evidenced by the Kaibab limestone Pk being broken into blocks of about a meter of less, with shearing in two directions- this leaves large fractures and fissures through the Virgin was able to exit the up-to-the-west rim along the fault. This rotation is very local, and possibly is the reason why the Virgin has captured the previous Laverkin and Ash Creeks drainages;

7. Previous to the dominance of the Virgin River (which flows west in the local area), there was generally SW drainage, shown by the Pc (Pleistocene conglomerates) at hiway 9 and Virgin Anticline NW limb intersection (this outcrop also shows that movement is continuing, since the previously flat gravel deposition is now dipping down to the south). Other Sw drainages occur at the Pc outcrop near the Virgin Power Plant in Laverkin, and along the present Virgin River at the Hiway 9 bridge;

8. Vulcanism accompanied uplift along the Hurricane fault, as seen by the multi-vents in the Hurricane-Laverkin area (and for the North Creek basalts). These flows were mainly basaltic at first, but later became more violent with several cones in the same area;

9. There is a thin ash layer covering a foot thick sandstone at the base of the local extrusives, and several tuffs now occur in the column, showing that ash falls not only preceded the basalt flows, but also accompanied them;

10.Basalt has served as dams for the present Virgin River, and has re-routed the river- as evidenced by canyons in the earlier basalts. Generally the river worked to the north of the dams, into the Triassic rocks, but occasionally the river broke through the basalts;

11. Dams created sluggish streams, one of which is shown by the Sky Mountain Golf course meander (whose direction was influenced by local NW-SE faulting);

12. Fracture orientations in several directions have influenced the courses of the Virgin River, indicating that there was a major stress change across the Hurricane fault. Generally the fracture orientation is N-S near the fault, but is more NW-SE (with accompanying orthogonals) away from the fault.

13. The Hurricane fault appears sinusoidal on the map presentation, and this is partly caused by the increase of "walking" in river canyons (Gould's, Honeymoon, and Virgin locations); and

14. The Hurricane cliffs appear regular in height and orientation, except for the Virgin River, where it appears that there is rotation, exceptional uplift and erosion, and cross-faulting.