H25: Laverkin Cliffs below Hurricane Mesa 3/15/06

There is an abandoned washed-out bridge, just off hiway 17 going to Toquerville from Laverkin, which formerly was the main bridge toward I-15. It overlies the Laverkin Creek, where there are tree limbs which can be used to cross the creek. This is brushy country along the creek, so is not an easy stroll. The creek was running briskly when we crossed it, and afforded a vigorous hike through the riparian zone.

This is the present drainage for the highlands in the Zion Park; it allows rocks eroded from the park to flow to the south to enter the Virgin River, over the cliffs of the Hurricane fault. Any rocks from the Pine Valley Mountains would have to cross the Ash Creek to the west, in order to get into this drainage. There are small cobbles of PV intrusives rocks (granite-like Monzonite) found in the conglomerates in the cliff walls- telling us that at one time there was no barrier like the Ash Creek to prevent their passage. This tells us that the Laverkin Creek is the oldest creek of the two, or that the Ash came later as the uplift of the H fault worked westward in splays that developed afterward. This is an important conclusion, since the splays we will see to the east are young- having uncemented sediments from the Pleistocene epoch.

Some excellent views of the Hurricane valley are seen from the top of the cliffs, after climbing about 200 feet in elevation change. This hike is not recommended for easy access, as there is much brush, steep slopes, and difficult climbs.

Hiking S 14 T42S R13W, there are several gravel pits or quarries in the east edge of Laverkin, where the creek has flowed in earlier times, when the canyon was much higher in elevation. These gravels- now conglomerates- were in the bottom of the creek, before the water cut the creek down to a deeper elevation. The soil has not had sufficient time to form rock, and I call the formations Pre-Stone (not Prestone, which is a commercial anti-freeze). All of this is Pleistocene in age, meaning that it is less than 1 million years old. This pre-stone is probably less than 100,000, and possibly even less than 10,000 years since that is the age of the last volcano. At any rate, the soil makes sharp ridges, so that it is slightly cemented; soil can convert to caliche in just a few years, when there is sufficient mineralization caused by desiccation (drying under the sun). Some caliche is as strong as concrete, and this all depends upon having CaCO3 available. For the case at hand, the limestone is just up the cliffs, in Pk or Permian Kaibab limestone; it dissolves out with acidic rainwater. But you can see that the soil has not the strength of the conglomerates in the Virgin River, where we found rocks which were formed recently, cemented with the dissolved lime from the Pah Tempe hot springs.

The river is very young in its present canyon, since we can see gravels and conglomerates spread over the whole area as we drive along hiway 17. It is apparent that the river is cutting down swiftly, not so much because of the abrasive contents, but because the land is falling relatively to the cliffs to the east, because of sinking of the whole Basin and Range (B&R)- especially in this location. We have seen on hikes to the west that fissures are opening in this area, due to rotation of large blocks of the stratigraphic column into the voided zone just west of the Hurricane fault. The fissures in loose soil tell us that the process is happening now (but the rate is only on the order of a millimeter yearly). Nevertheless, this can affect man’s operations, since cracks will develop in concrete slabs in the lifetime of a house. It is best not to buy real estate bordering on the cliffs above any of the creeks in the transition zone 1-2 kilometers west of the Hurricane fault.

What we would like to find on this hike are indications that faulting is occurring down to the east or SE, as opposed to that we can see just to the SE- where faulting is of the normal type. A normal fault has the downthrown rock dragging upward along the fault as it falls. We know that for the cases where Lava has voided space near volcanoes, the Mesozoic sedimentary rock column rotates down to the east, causing hogbacks to appear to the west, in monoclines. This occurs near volcanoes, and we are not sure that there is a volcanic neck or vent near enough to this location to effect this. There are several flows near by, but they may have flowed down from the north. It will be obvious that the faulting has reversed the known trend, when we find the faults going down to the east.

The questions we are trying to answer today include:

1. Do the intrusive dikes found last week extend in influence this far to the SE of the PV Mountains to cause the disruption here?

2. Is the main entity causing the Toquerville Pk mountain (to the NE of the town, where the radio towers occur) to rise above surrounding Pk outcrops to the 5000 foot elevation, and creating an anticline-like disruption, due to this dike (which could still be underground, not visible)?

3. If the above are found to be positive, can this have also caused the Hurricane fault to bifurcate- yielding two valleys with large faulting and two significant drainages (Ash and Laverkin Creeks)?

4. Can the influence of the SE-ward trending intrusions have also reached far enough to yield the fissures and NW fractures in the rim of the Virgin River, as shown by the fracture trends in the Kaibab limestone there (this would be on the order of 10 miles- near the town of Virgin)?

5. If the above suspicions are found to be true, what can have caused the SE trending dikes to have moved this far from the PV Mountains proper, except for the omni-present NW-SE fractures?

We found that there are no obvious reversals in dip of the sedimentary blocks seen on this hike. Rather, all of the Mesozoic and younger rocks either dip down to the north or to the west. The dip down to the west would be the normal, since the H fault is opening and dropping to the west creating elevation differences into which the rocks on the cliffs to the east slump or drop. However, the dip down to the north is unexpected, particularly when there is an angular unconformity with other beds of similar age. These blocks indicate different rates of drop due to differential uplift (or down drop).

Nowhere did we see the rotation of blocks CW, looking northward, which occur near the Virgin and Honeymoon Creek outlets; but then neither did we see volcanic vents which are expected to create the weak zones, into which the blocks rotate. We did see many angular unconformities which indicate different rates of downdrop to the west. Therefore, we answer the questions above as follows:

I. Answers to the questions above are not found in this location, but we must continue to the highlands east of Toquerville, to look at the faulting there.

II. It appears that the location of the highly faulted zone, containing the many minor splays of the H fault, is suspiciously near the trend of the SE-trending intrusive rocks, and we must get closer to the PV Mountains to make a conclusion.

III. Upon looking to the NW, it appears that there is a local high which could be the surface manifestation of the not-yet-exposed underground Monzonite. Geophysics must be used, or well logs analyzed to find whether there are underground intrusions, not yet exposed by erosion as are the PV Mountain and their foothills.

IV. There are many splays of the N-S faults parallel to each other, east of the main H fault. I take it that these are young slumps and slides, caused by the elevation difference between the Hurricane Mesa and the transition zone (because of the lack of cohesion of these sedimentary rocks). The reasoning is that the rock has turned to soil, because of the constant sliding downhill. No importance will be given to these parallel sliver faults, since they show no new trends, and are complex because of the slumping into the weak zone. It is still possible that the slumping zone is initiated by the SE-trending intrusions from the PV Mountains. Nowhere else does this occur along the H fault, to this degree.