GEOLOGY FIELD ASSIGNMENT

by

Cydnee Sciacqua

Rock Types – Igneous, Metamorphic, and Sedimentary

Sample Collection Sites

Basalt – Outside of Millerton Lake Park

Igneous

Olive Basalt – collected outside Millerton Lake Park. In this area you can also find granite pegmatite with lots of muscovite, occasional tourmaline and red garnets. The area is estimated to be about 60,000,000 years old. This sample is dark gray on the outside and black on the inside, there are some white specks layered within the sample. A few metallic specks. This sample has a smooth outside, but a rough, slightly jagged inside where it fractured away from the larger sample.

Sample Collection Sites

Granite and Schist – Sky Harbor Road above Table Mountain Casino

Igneous

Granite – collected above Table Mountain Casino on Sky Harbor Road. In addition to granite, you can see some areas of schist and in places you can see a resistant cap rock on top of the hill that weathers and pools down by the road, this is lava rock from the Table Mountain lava flow. The area is estimated to be about 60,000,000 years old. This sample display characteristics for pegmatite and appears to have quartz, hornblende, orthoclase, and feldspar. The surface texture is rough and course-grained.

Metamorphic

Schist – collected above Table Mountain Casino on Sky Harbor Road. In addition to schist, you can also see granite and in places you can see a resistant cap rock on top of the hill that weathers and pools down by the road, this is lava rock from the Table Mountain lava flow. The area is estimated to be about 60,000,000 years old. It’s hard to see, but mostly dark gray in color with curvy band of burnt orange / rust running through it (possibly limonite). This sample’s surface is smooth all the way around.

Sample Collection Sites

Breccia and Sandstone – State Route 145 West of State Route 41

Sedimentary Breccia – collected west of

junction State Route 145 and State Route 41. I collected this sample from along side the roadway on State Route 145. The area is part of the Sierra Nevada upland and is a remnant of the late Miocene Landscape. This sample has includes many local rocks (granite, basalt, gneiss, etc.). The difference between breccia and conglomerate is that breccia has angular fragments of rock particles and conglomerate has rounded fragments of rock particles.

Sedimentary Sandstone – collected west of

junction State Route 145 and State Route 41. I collected this sample from along side the roadway on State Route 145. The area is part of the Sierra Nevada upland and is a remnant of the late Miocene Landscape. Rock is burnt orange / rusty brown in color, very dull in complexion. Resembles hardened sand. The color implies that this sample could have limonite and hematite in it. There is a light colored layer between the top and middle exposed on one side of the sample.

Faults

The San Andreas Fault is a continental transform fault which runs a length of 810 miles through California. The fault’s motion is right-lateral strike-slip (horizontal motion). It forms the tectonic boundary between the Pacific Plate and the North American Plate.

Town of San Juan Bautista

The town of San Juan Bautista and the Mission rest on the fault line. The fault’s presence can be seen in the undulating and angled streets of San Juan Bautista. In 1906, there was a violent earthquake which shook the greater part of central California. The sidewalls of the Church collapsed and were restored in 1976.

San Juan Bautista Mission – View From Cemetery

The San Andreas fault runs along the base of the hill below the cemetery. The cemetery is accessible from the inside of the north side of the church. Vestiges of the original El Camino Real trail can still be seen north of the cemetery.

Mission view from other side of wall

In the bottom two photos you can see the scarp that was created from the fault line.

Mechanical (physical) Weathering

Mechanical (physical) weathering is accomplished when physical forces break rocks into smaller and smaller pieces without changing the rock’s mineral composition.

Tree growing up through rock

Talus at the base of a mountain

Chemical Weathering

Chemical weathering involves a chemical transformation of rock into one or more new compounds. Examples of Chemical Weathering can be seen around us. Here we can see two gravestones placed within a year of each other, one is legible and the other is difficult to read.

Parrish J. Robert 1938 – 1988

Clarice V. Dibble 1904 – 1989

Yosemite National Park

Erosional forces acting upon different types of uplift-created joint and fracture systems are responsible for creating the valleys, canyons, domes, and other features we see today. Half Dome (center of picture) was created by such erosional forces and is an example of an exfoliation dome.

Mass Wasting

Talus form at the base of a mountain.

Gravity caused rock to break free leaving the uneven face on this formation.

The face of El Capitan, a prominent granite cliff that overlooks the Yosemite Valley, was created by mass wasting.

Erosional Forces

A tributary glacier created the u-shape of the Yosemite Valley.

Bridal Veil Fall patiently works on eroding the side of the mountain and the rocks below.

Sedimentary Environments

Continental - Environments which are present on the continents, such as alluvial fans, fluvial environments (rivers), lacustrine environments (lakes), aeolian or eolian environments (deserts), and paludal environments (swamps).

Transitional – Environments at or near where the land meets the sea. Transitional sedimentary environments include deltas, beaches and barrier islands, lagoons, salt marshes, and tidal flats.

Marine – Are in the seas or oceans. Marine environments include reefs, the continental shelf, slope, rise, and abyssal plain.

Continental Environment – Friant, CA

Lakes (lacustrine

environments) are diverse. They can be large or small, shallow or deep, fresh water or salt water. Mudcracks, wave ripples, laminations, and varves may be present. Fine sediment and organic matter settle and produce laminated oil shales.

Continental (continued)

Transitional Environment – Carmel, CA

Beaches are shoreline deposits exposed to wave energy and are dominated by sand with marine fauna.

Marine Environment – Monterey, CA (behind the Monterey Bay

Aquarium

Reefs are wave resistant, mound-like structures made of the calcareous skeletons of organisms like corals and different types of algae. Most reefs are warm, clear, shallow, tropical seas. Continental shelf is the flooded edge of the continent. It is relatively flat, shallow (between 200 ft and 600 ft), and can be hundreds of miles wide. Continental shelves are exposed to waves, tides, and currents, and are covered by sand, silt, mud, and gravel.

Friant Dam

Friant Dam is a concrete gravity dam on the upper San Joaquin River, in the Sierra Nevada foothills, between Fresno and Madera Counties. The dam was completed in 1942, forms Millerton Lake and was built by the U. S. Bureau of Reclamation.

Friant Dam and Millerton Lake

The lake and dam are about 15 miles north of downtown Fresno. The lake’s storage capacity is 520,500 acre-feet, used for irrigation of the San Joaquin Valley and is distributed by the Madera and Friant-Kern Canals. Flood control and recreation are secondary uses for the lake and dam. Big Creek hydroelectric system is upstream from the dam. The 25-megawatt Friant Power Plant in front of the dam produces hydroelectricity for the Friant Power Authority.

Questions and observations are welcome

Thank You