H26: Above Toquerville, Ash Creek S35 T40S R13W 3/22/06

This hike is an easy one in terms of access, duration, and convenience. It transpires in the upper reaches of Ash Creek, NE of Toquerville S35 T40S R13W. There is a mostly paved road, starting north at the Ash Creek Bridge, south side, in downtown Toquerville, which follows the creek until public lands are reached. The springs and lands by the paved road are privately owned, so continue driving on the gravel portion until a high valley is reached, where parking exists for many cars. This will be at the fork in the road as well as in the creek drainage. A very rough gravel road continues eastward to the Laverkin drainage, but park at the junction, where one can climb onto the contact of the Paleozoic Pk and the younger lavas and Mesozoic rocks.

The area of investigation lies astraddle the contact of rocks separated by a splay of the Hurricane fault, H-flt. The Paleozoic Pk (Permian Kaibab limestone) is shoved up at a 30-45 degree angle to the west, partly by the Laramide compressional event (<100 mybp, million years before present), but also speculatively by the much later, 21 mybp Miocene Intrusion of the Pine Valley PV Mountains. It is seen by comparison with the Quail or Virgin anticline, that compression created folds with axes of NE-SW orientation, whereas the Pk peak has a larger inclination than the anticline proper, with axis perpendicular to the Laramide creation from the Miocene. The extra shove from the Miocene intrusion can be noticed to take affect at the peak above the creek bifurcation, as the dip of Kb changes from <30 to > 30 degrees up dip to the NW at the highest point of the mountain. I think that the Pk peak has been further aggravated by the uplift of the PV intrusion- which is nearby. This hike is planned to find any evidence of this second �shove�. Evidence could be the presence of dikes nearby or the re-orientation of the Virgin axis (taking a turn to the SE, or being shoved away from its track to the NE, by the later event occurring after the Laramide).

The first obvious entity at the high valley is that of a contact of Pk and Pleistocene basalts oriented N-S lying below the Pk peak. After emplacement of the young basalts, the basalts have dropped to the west along the H-flt trace, leaving black rock along-side limestone. The black basalt is less than 1mybp, whereas the Paleozoic rocks are on the order of 300mybp. This represents volcanic-emplaced rocks coexisting near marine limestones (with fossils of crinoids� stems, brachiopods, and bryozoans). This is a steep climb of about 100 meters, but the view is worth the effort to see the �Big Picture� of the H-flt as it creates a scarp to the south. The drainage here is toward the Ash Creek, whereas on the east side of Pk peak there is Laverkin drainage. Both of these creeks are dominated by the paths of the various splays of the H-flt.

Pintura 7.5 minute TOPO map shows the following features, without knowledge of geological considerations:

1. The trend of the main Hurricane scarp is N-S, until the Pk peak at the 5265 feet Radio tower is reached; then northward, the trend is NNE;

2. The trend of hills west of the Hurricane fault weak zone is also N-S, including Beatty Hill, mine and dikes investigated in H24 hike, and the monocline near the Laverkin-Virgin confluence (a problem with using Beatty Hill as a reference to N-S linears along the H-flt is that it is at lest 5 miles from the main fault, whereas all other N-S features investigated occurred no more than 2 km distant);

3. The Wet Sandy Creek lies on an almost linear SE-NW trend, indicating that the dikes to the north have shaped it to conform to the progression of dikes- which probably were conformal with the NW-SE fracture trend of Miocene times;

4. Wet Sandy drains into the Ash Creek at the valley below the Pk peak; and

5. Although the Pk peak is isolated by the parallel valleys of the Ash and Laverkin creeks, a spring occurs at the locus of the intersection of the disruption (change of orientation) of the Hurricane fault and the SE trend of the Wet Sandy. Of course, a spring is indicative of drainage from higher elevation, and Pk peak is certainly that, but a spring is also indicative of a barrier which causes the water to emerge- such as an impermeable fault face or a fracture orientation change.

All of the above suggest that there is a major change in the subsurface stress pattern, near the Toquerville Springs. I have found that springs often appear whenever a major discontinuity in either rock type or fractures, or faults in the subsurface, occurs. A good example I found in the last few years was in Verde Valley, at the Winter Cabin Springs, where a change in Pliocene Verde limestone fractures from N-S to NE-SW orientation occurred. The spring had an anomalous composition, containing unusual K, salinity, and TDS. Others of this type contained unusual F, B, and acidity. This spring flowed from young fractures in Pv, which has fresh water limestones of less than 5 mybp, and must have occurred as a result of fractures less than this age.

The questions we are trying to answer for this hike include:

a. Are there reversals in the fault planes or stratigraphic dips, in the valley below the Pk peak and further to the south after turning on the south fork of the road?

b. Do we find confirmation that there is rotation of the blocks CW into the fault plane to the east (looking north at a X-section)?

c. Is there any suggestion that the row of intrusive dikes, which pointed in general from PV Mountains to the Pk peak, continue closer to Pk peak, in the subsurface? If so, there would be a hint of a NW-SE high of uneroded rocks pointing toward Pk peak. This would likely occur NE of the Wet Sandy creek.

d. Do the main saddles contain evidence of major faulting going through the area?

e. When we see red rocks butted against limestone, we know we have Mesozoic lying next to Paleozoic- what is the angle of dip for these abutments?

The answers to a. and b. are no, and we found that the dip was down to the west (a CCW rotation into the fault zone), fairly consistent at about 70-80 degrees. We found one loose block of slickensides, indicating that there was indeed sliding along some fault planes, but mostly the Mesozoic seemed conformal with the underlying Permian Kaibab limestone, Pk. The dip of Pk can be seen to change abruptly near the top of the east exposure, from almost flat to 60 degrees down to the west near the ridge line.

When returning from the south, walk along the creek bed, and you will find outcrops of Moenkopi, Trm, containing pseudomorphs of gypsum roses in a limey member. These pink �roses� grow with time, as groundwater which is saturated with CaSO4 precipitate out gypsum onto some nucleating sites within the rock. These are still in place and will be ruined if you try to pry them out; they are excellent for photographing however, since the color contrast is striking. The gypsum is softer than the limestone, and is best left untouched for future hikers to enjoy. You will probably find samples of 2-3 inch roses in the creek bed, which are easily carved for improvement.

Answers to c. and d. are yes, and the dip is generally greater than 60 degrees down to the west; the line of intrusives approaches this area, but must be in the subsurface by the time it reaches this valley. There is a remnant high in the basalts on the west side of the valley, which could be the result of a more resistant subsurface (possibly igneous rock), but this has to be explored further. Saddles generally indicate fault planes locally, but some faulting is so young that the creeks drain below the fault planes.

The only new information found for this area was on the published geological quadrangle For Toquerville, where there is shown some NW-SE faulting proceeding toward Wet Sandy Creek from the weak zone area north of Laverkin. These fault slivers by extrapolation would align with the Toquerville spring and a saddle between Monzonite dike hills. This would give some credence to my epiphany that the NW-SE Wet Sandy Creek is the real boundary of my simple Model for the Hurricane fault.

There was no new evidence of confirmation of the Hflt Model- all dips being regular (down to the west) and fairly monotonous. Although this area is a boundary (discontinuity) to my Hurricane Model, the surface Geological Boundary will have to be sought further north in Intrusive rocks.