Natasha Sramek Field Assignment Geology 103, Summer 2015 Lake Tahoe Community College

1. Lake Berryessa
Geology Field Assignment
Natasha Sramek
(Lake Berryessa Fishing, n.d.)

2. 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

3. 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.

4. 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)

5. Great Egret
Ardea 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

6. Changes through Time, the Flora
California Blue Oak,
Quercus douglasii

7.  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

8. 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.

9. 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.

10. 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.)

11. Relative Dating Principles
(Great Valley Sequence, n.d.)

12. 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.

13. Unconformities Present at Lake Berryessa
 Sedimentary layers on
top of one another

14. 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.

15. 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.