Lake BerryessaGeology Field Assignment

Natasha Sramek

(Lake Berryessa Fishing, n.d.)

Lake Berryessa, California

Located in Napa County, California and is surrounded by vast mountains ranges

Coordinates: 38.570938 ° N, 122.23526°W

Putah Creek is the largest body of water flowing from Lake Berryessa and is often used for agricultural purposes on UC Davis campus and the surrounding area

Geological Background

Most of the central valley in Northern California consists of sedimentary rocks and volcanic rocks left behind from a subduction zone, where the Pacific seafloor plate is subducting beneath the North American continental plate.

This caused a large chain of active volcanoes that later eroded and washed offshore into layers of sand, boulders and siltstone. The Sierras are the “exposed roots” of the volcanoes and Lake Berryessa along with the Sacramento Valley is the offshore sediment (Alden, 2012).

The thick layers of sedimentary rocks found all over Lake Berryessa are estimated to be 13 kilometers thick, and represent about 80 million years of erosion.

Changes Through Time, the Mountain Ranges

The Mountain ranges surrounding Lake Berryessa formed 150-130 million years ago during the Mesozoic Era

Consists mostly of sandstone and shale, forming the Great Valley complex as several layers of mud and sand accumulated in the Continental Shelf along North America (Lake Berryessa – sedimentary rocks, 2006)

Great EgretArdea Alba

Great Egrets are commonly seen in North America in both freshwater and saltwater habitats, usually sanding while hunting for fish. They are white with yellowish-orange bills and long black legs.

They are rather ancient birds, first fossils found date about 7 million years ago, the late Miocene (Great Egret, 2005). Through DNA hybridization, these birds have been traced to the Ciconiformes order, along with herons, storks, and spoonbills just to name a few.

Due to the lakes, ponds, marshes and other bodies of water Egrets hunt in, their long necks and legs were selected for to wade into shallow waters for hunting. I saw a few of these majestic birds while at Lake Berryessa, they are stealthy and swift when hunting!

The Great Egret’s diet consists of fish, amphibians, and some insects. Their bill has adapted to seizing small prey quickly and swallowing them hole.

(Great Egret, 2005)

Changes through Time, the Fauna

Changes through Time, the Flora California Blue Oak,

Quercus douglasii

The blue oak is native to the state of California and is one of the largest ancient forests remaining.

It covers about 3 million acres along the ocean ranges, the western foothills, and the north slope of the San Gabriel Mountains.

Blue oaks have adapted well to droughts and very dry environments, surviving weeks without water. This was allowed by their extensive root systems. Over time, blue oaks have adapted to survive by reaching 80 feet to ground water levels if needed.

The thick, light colored bark was chosen for to remain hydrated and to reduce fire damage during droughts and wildfires. Blue oaks easily reproduce through seeds, but also can through cut stumps or burnt vegetation. They have developed over a very long period of time to be very resilient in harsher environments.

California Blue Oak

Conglomerate

A sedimentary rock made up of a mesh of smaller, round rocks similar to gravel.

This massive rock was found at Lake Berryessa shows a massive amount of weather as seen by the discoloration.

Conglomerates can be any combination of rocks and minerals. Here, I believe there is lighter sandstone mixed in as well. It gives the rock a more yellow hue.

Limestone, a Sedimentary Rock

Limestone is a sedimentary rock commonly found in warm, marine environments. It is usually formed from compacted shells, coral and other organic material.

A ton of shells are present on the shores of Lake Berryessa as well as an abundant amount of this soft, light gray sandstone.

There are many different types of sandstone, and I think the most abundant is the chalk type based on the color and texture.

Serpentinite and Serpentine Soils

Serpentinite is a type of ultramafic rock and is formed from the force of the Earth’s crust as it moves. The gray-green color comes from when water flows through the cracks, changing the mineral’s chemical make-up

“Serpentine” is commonly used to include both serpentinite and peridotite (Serpentine Soils and Plant Adaptations, n.d.)

Soils containinty serpentine, like at Lake Berryessa, provide very extreme environments for plant life. There is a large amount of magnesium and heavy concentrations of heavy metals with very poor calcium and nitrogen intake. This combination provides not enough nutrients and reduces root growth. Plants that flourish in serpentine soils have developed adaptive strategies to tolerate this harsh environment (Serpentine Soils and Plant Adaptations, n.d.).

(Serpentine Soils and Plant Adaptations, n.d.)

Relative Dating Principles

(Great Valley Sequence, n.d.)

Law of Superposition

The previous picture shows a turbidite, one of many easily identified at Lake Berryessa. They occurred when shale, mixed with clay, was suspended in in the water and settled out on the deep ocean floor, during a sudden, high density event.

It is visible that these layers are in a horizontal fashion, with the oldest layers on the bottom. This follows the Law of Superposition as more sediment gets deposited.

The Law of Superposition is important when determining what has happened in the past. Each layer can be dated numerically to establish relative ages of the rocks and fossils within each layer.

Usually rock layers are deposited horizontally, so when they are found in the tilted position like seen in the photo, geologists can determine specific events, or s series of events of what would have caused the layers to tilt. The layers in the photo may have been tilted due to an Earthquake, which are very common in California due to the strike-slip fault famously named the San Andreas Fault.

Unconformities Present at Lake Berryessa

Sedimentary layers on top of one another

Disconformity

This unconformity was very visible from the road, much like many other geological landscapes found at Lake Berryessa. The roads are constructed so that they take you through the park in a very windy fashion.

I determined this as a disconformity due to the distinct parallel layers of sedimentary rock. The erosion that occurs is very distinct, with the older layers of rock buried under younger horizontal layers. Just by sanding on the side of the road, the wind can be seen taking away sediment. Due to the consistency of the rock layers and the sandiness, I think these are sandstone layers arranged with larger pieces of limestone layers.

Within this disconformity, there may be layers of shale, sandstone, limestone, conglomerate among other rocks that are not as easily identifiable in the Lake Berryessa landscape.

Reference Page

Alden, A. (2012, January 26). Geological Outings Around the Bay: Mount Vaca and the Monticello Dam. Retrieved July 31, 2015, from http://science.kqed.org/quest/2012/01/26/geological-outings-around-the-bay-mount-vaca-and-the-monticello-dam/

Blue Oak – Quercus douglasii. (n.d.). Retrieved July 17, 2015, from http://www.blueplanetbiomes.org/blue_oak.htm

Great Egret. (2005). Retrieved July 6, 2015, from http://www.allaboutbirds.org/guide/Great_Egret/id

Great Valley Sequence. (n.d.). Retrieved July 18, 2015, from https://en.wikipedia.org/wiki/Great_Valley_Sequence

Lake Berryessa. (n.d.). Retrieved July 13, 2015, from https://en.wikipedia.org/wiki/Lake_Berryessa

Lake Berryessa Fishing, Lake Berryessa CA. (n.d.). Retrieved July 13, 2015, from http://www.californiafishingonline.com/lake_berryessa.html

Lake Berryessa - sedimentary rock (sandstone and shale). (Aug. 18, 2006). Retrieved July 12, 2015, from http://geomaps.wr.usgs.gov/sfgeo/geologic/stories/berryessa_sedimentary.html

McLaughlin Natural Reserve. (Oct. 25, 2007). Retrieved July 14, 2015, from http://nrs.ucdavis.edu/mcl/natural/geology/

Minerals. (n.d.). Retrieved July 15, 2015, from http://www.minerals.net/mineral/serpentine.aspx

Serpentine Soils and Plant Adaptations. (n.d.). Retrieved July 15, 2015, from http://www.fs.fed.us/wildflowers/beauty/serpentines/adaptations.shtml

What is Relative Dating? (2003). Retrieved July 30, 2015, from http://study.com/academy/lesson/what-is-relative-dating-law-of-superposition-principles-of-original-horizontality-cross-cutting-relationships.html

Wilderness - Cedar Roughs Wilderness - General Information. (n.d.). Retrieved July 14, 2015, from http://www.wilderness.net/NWPS/wildView?WID=685&tab=General

Photo Credits given to Natasha Sramek when not cited by another.