The Old Marysville Buttes EarthCache

Welcome to the Sutter Buttes

This cache is accessible via public roads. Hiking access to the Buttes is restricted, see below. You do not need to go to the Posted Coords.
Use the additional waypoints below for access to this Earthcache.
There is a nice place to pull off and park your car for the first stop. The second stop can be completed from the car.

The Sutter Buttes’ volcanic spires rise over 2,000 feet above the valley floor.  Formerly known as the Marysville Buttes, the now renamed Sutter Buttes is located about 50 miles north-northwest of Sacramento and 11 miles northwest of Yuba City.  It is the only volcano in the valley.  It is formed by a central core of volcanic domes and then surrounded by large fragments of volcanic debris.  This volcano was most active during the Pleistocene Period, about 1.6 to 1.4 million years ago.  

The Geology 

The majority of time during the last 75 million years the Sacramento Valley, also known as the Great Valley, was a very shallow sea connected to the Pacific Ocean.  Sediment carried by rivers from the Sierra Nevada and Klamath Mountains were deposited over time in this seabed.  The sediment compacted and formed giant layers of sandstone and marine shale.  As the area rose in sea level over millions of years, the area was mostly flat plains with the Sacramento, Feather, and San Joaquin River dominating the landscape.

Today when we look at the Sutter Buttes we see 3 main sections: the castellated core, the moat, and the rampart.  The castellated core is made of very high peaks and is located in the center of the Buttes.  These peaks were formed when partly molten rock, called magma, rose to the surface as think, sticky plugs. These first formed a steep-sided volcanic feature called domes.  Today, large portions of surface material that covered the domes have eroded away exposing the interior rock layers.

The moat surrounds the castellated core.  The moat is comprised of a ring of low valleys and is filled with an underbelly of sedimentary rocks. These rocks are much older than the Sutter Buttes volcano.  The rocks that make up the sedimentary debris are mostly shale, sandstone, and conglomerate that are from between 70 million years ago and 2 million years ago.  The layers of sediment in the moat were uplifted and tiled steeply when the volcanic domes and castellated core began forming which allowed the softer shale and sandstone to erode away, forming the moat.

The Rampart consists of the outer part of the Sutter Buttes.  This broad, low, outward sloping hill area was formed by flows of fragmented volcanic debris that moved away from the source (the castellated core).  Some material was so hot it caused explosive eruptions while other material slowly fell off the cooler outer parts.  This material is what is deposited alongside the moat.

_{USGS Geological Map of Sutter Buttes Volcano}

Volcanic History

The volcano at the Sutter Buttes first began erupting about 1.6 million years ago early in the Pleistocene age.  Magma pushed upward through the thick sediments of the Great Valley and eventually breached the surface.  This formed the domes of the castellated core.  As explosive eruptions took place, (caused by an abundance of gas pockets below the surface) some magma became pulverized and was deposited into blocky fragments and volcanic ash which eventually hardened.

Between 1.6 and 1.4 million years the Sutter Buttes continued to erupt.  As the eruptions continued the mineral composition of magma changed which further altered the landscape.  Toward the beginning the lava was poor in magnesium and iron but rich in silica, potassium, and sodium.  This made the lava very thick and sticky which formed the initial domes.  After 30,000-100,000 years, the mineral composition of the lava changed and it lost some of its think stickiness because it was lower in silica but higher in magnesium and iron.  This formed larger domes when it erupted through the numerous vents already formed in the castellated core.  Additionally, much of this lava also spread underground lifting the old layers of sedimentary.  Layers that originally were horizontal were lifted and bent into vertical positions.  This type of eruption continued until 1.4 million years ago which created the mountainous interiors of the Buttes.

During times of violent explosions, dome rocks were fractured into fragments ranging from ash to giant blocks.  This material was carried down the slopes of the domes by pyroclastic flow (a slurry of debris that moves much like a landslide but caused by hot volcanic gas).  The hot pyroclastic flow would accumulate with cooled water in the moat eventually forming the outward-sloping rampart.

The Buttes Today

From about 1.4 million years ago to today not much has changed with one exception: erosion.  Rain, running water, wind, and human interaction have cut through the softest and weakest materials.  Streams and landslides penetrated the weaker shale and sandstone deposits exposing them to the moat valley.  Streams that flow out of the Sutter Buttes have also cut through the pyroclastic debris layer forming radial valleys throughout the rampart.  

Why Are They There?

This question has been tackled by scientists since the early explorations of the Buttes.  There is much debate over the related mountain range — is it related to the Cascade Range to the North or to the Coast Range to the Southwest?  Either way, the Sutter Buttes does not easily meet the trends that make up either region.  Recent studies have begun leaning towards it being a member of the Coast Range due to the composition, texture, and age of the volcanic rock.

But why, in the middle of a huge valley, did an eruption take place here?  Why not further south?  Studies have revealed a north-south ridge with  high level of magnetism and gravity deep beneath the Valley floor, and, most importantly, beneath the Buttes.  Perhaps this is due to an inactive fault buried deep below?  No matter what, the Sutter Buttes provides a unique and remarkable geologic feature of Northern California’s Great Valley.

The Routes

The Faster way:

1. Leaving Stop 1 - head west on S Butte Rd.
2. After .75 mile - turn right on W Butte Rd.
3. After approximately 4.1 miles - turn right on Pass Rd.
4. Continue approximately 3.75 miles to Stop 2 (on your left).

Through the town of Sutter:

1. From Stop 1 head East on S Butte Rd.
2. After approximately 3.6 miles - turn left on Acacia Ave.
3. After approximately 1.15 miles - turn left on Pass Rd.
4. Continue about 3.25 miles to Stop 2 (on your right).

To log this cache:

In an email please answer the following questions based on your personal observations:
Do not post answers as part of your log, encrypted or otherwise, or it will be deleted!

At Stop 1:

1. To the your south is the Sacramento Valley. To the North lies the rampart of the Sutter Buttes.
2. Look due South and denote the topography. Now look due North and denote the topography. Describe the difference between the two.
3. Looking due North: Do you notice any large clusters of boulders scattered across the hillsides?

At Stop 2:

• You are currently in "The Moat" of the Sutter Buttes. You do not need to stop your car to get the answers to these questions, however there is a very small roadside pullout should you need too. Just be careful exiting your vehicle.

4. Now looking due South do you notice any large clusters of boulders scattered across the hillside and landscape? What does this tell you about the direction the explosion 1.6 million years ago?
5. Compare your answers between questions 3 and questions 4.
6. Look due North: You'll see a stone outcrop. -- Describe the way the stone jutts out of the mountain. What direction does this outcrop face?

• Optional: take picture of yourself at Stop 1
• While your in the neighborhood for stop 2, why not check out the The Sutter Buttes Quadrangle Cache - GCYCK5. It's sure to bring a smilie to your face :)

Congrats to the four ladies: magpup, mrs.tanky, tufbill and rubberpaws for FTF!!!!