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Regional Geologic Sites of Interest
Have you ever seen what the flanks of a 23million-year-old volcano look like after having traveled hundreds of kilometers along the San Andreas Fault? If not, it is imperative that you read more! This field trip focuses on areas where nature has formed the landscape into beautiful and periodically hazardous canyons, faults, and volcanoes. The trip begins in the Salinas Valley, and takes you south to the actively eroding Arroyo Seco canyon, and then across the valley to the Pinnacles National Monument. The dynamic relationship between depositional, erosional, and tectonic processes of ancient and modern environments will be analyzed.
Point Lobos State Reserve
Point Lobos State Reserve is conveniently located just off Highway 1 south of Carmel Valley. The two main geologic highlights of this fieldtrip are the Eocene turbidites of the Carmelo Formation and the unique granodiorite porphyries of the Monterey Mass. The uplifted submarine canyon deposits of the Carmelo Formation provide a glimpse into the past as well as clues to the depositional processes now occurring in the nearby Monterey submarine canyon. This trip also offers the geology student an opportunity to compare the Cretaceous granites of the Monterey Mass to those in the Gabilan Mass and come up with a hypothesis as to how each formed.
Santa Cruz Coastline
Tucked into the northern part of Monterey Bay is the town of Santa Cruz. It is known for its generally mild, Mediterranean-like climate, laid back lifestyle, excellent surfing, well-developed marine terraces, and beautiful coastline. On this field trip, the focus is on the present day coastline and coastal deposits of the past. Not only is the Santa Cruz coastline an excellent area to study the marine geology of the past, but it is an excellent area to study how coastal processes effect humans and vice versa. For instance, retreating cliff faces at Capitola Beach and riprap-protected cliffs at Steamer Lane provide dramatic examples of the constant pressure exerted by waves along this coastline. This trip focuses on two marine deposits, the Purisima Formation and the Santa Cruz Mudstone, deposited from the late middle Miocene to the Pliocene. These formations represent two different marine depositional environments that offer clues about oceanographic conditions, marine life, and sea level changes of the past.
Santa Lucia Range
The Big Sur coastline is one of the most spectacular coastlines in the United States, with amazing views, uncrowded beaches, and hairpin turns along Highway 1. This area owes much of its beauty to the tectonics of the region. Rapid uplift along thrust faults, such as the Sur-Nacimiento Fault, is responsible for the steep cliffs and partially-formed marine terraces that you will see on this tour. The dynamic up and down movement associated with these thrust faults has also created basins in which Paleocene marine sedimentary deposits, such as those found in the Indians Ranch, have been uniquely preserved.
Fremont Peak State Park
Want some perspective on the sequence of sea level changes and tectonic forces that shaped the Monterey Bay region? Then make an excursion up to Fremont Peak, on the north side of the Salinas Valley for a panoramic view of prominent formations. From the top of the peak you will see the Sierra de Salinas, the Santa Lucia and Santa Cruz mountains, Pleistocene dunes near Fort Ord, the San Andreas Fault and more. The white rocks exposed and scattered about on Fremont Peak are marble remains of a Jurassic seafloor, and beneath that is a mass of granite from the late Cretaceous (65 mya). How can an older formation be on top of a younger one? The granite pushed up from beneath, baked limestones into marble, and uplifted older layers. Eventually, they eroded from the hillsides leaving characteristic "roof pendants" sitting like caps on the mountains. The Oligocene Pinecate Formation is exposed in several road cuts on San Juan Canyon Road. This massive arkosic sandstone bed is orange to buff-yellow or brown and interbedded with a conglomerate of volcanics, carbonates and weathered granites. According to Clark and Reitman (1973), this was a shallow marine deposit with a proximal source to the west. The Zayante/Vergles fault is visible in eroded areas.
Santa Cruz Mountains
The dramatic rises and falls of sea level are recorded by the Tertiary sediments of the Santa Cruz Mountains. These sediments are primarily thick to massive turbidite deposits, composed of arkosic sandstone and mudstone clasts. The sandstones originated from the Ben Lomond Mass, part of the Cretaceous Salinian Block. This granitic terrane was modified in the Oligocene and Miocene times by wrench fault tectonics, forming a series of uplifted areas and depositional basins. During times of high sea level, some of the basins contained submarine canyons, which channeled the turbidites that are evident today. The Eocene Butano Formation is one such flow that represents a mid-fan deposit from a submarine channel (Stanley, 1990). According to Stanley (1990), physical evidence from the pebble, sand, and silt layers suggest that the sea floor was east of its present location.
Monterey Formation
Monterey & Santa Margarita Formations, the Navy & Chupines faults and Paso Robles Formation Landslide
The porous white layers of the Monterey Formation are composed of silicas from diatoms and radiolarians that flourished in the Miocene (11mya) during periods of strong upwelling. These were bathyal deposits in which fish bones and foraminiferans were fossilized and preserved. Today, the thin laminations have metamorphosed into opal A, opal CT, and porcellanite. The Monterey Formation and overlying Santa Margarita sandstones are fractured in this area by the Monterey Bay Fault zone, which includes the Navy, Seaside and Chupines Faults. These faults are active and extend offshore.
