By: Jean Reyes

I have chosen a certain number of rock types

that I have found near my job location. I have

chosen these rocks by color, shape, crystal

structure and, geographic location.

Although these rocks are different, most should

have similar historical background as they are

from the same area.

The rocks I have chosen are from a coastal area

located near San Miguel, C.A. at Camp Roberts

Military Training Center near the Santa Lucia

Mountains, where I am currently employed.

Camp Roberts is located near the Salinas

River between Monterey and San Luis Obispo

Counties.

It is named after Harold W. Roberts, a World

War 2 medal of honor recipient.

It’s surrounded by the unincorporated

communities of San Miguel, Heritage Ranch

(Lake Nacimiento), and Bradley. Its closest

incorporated city is Paso Robles, 12 miles

south on HWY 101.

The rock of the Santa Lucia's is dominated by the granitic basement of the Salinian Block, between the San Andreas Fault and Sur-Nacimiento Fault. According to plate-tectonic theory, the core of the Salinian block formed as part of the same batholiths which forms the core of the Sierra Nevada Mountains and the Peninsular ranges of Baja California. It was broken off the North American plate and transported north by the action of the San Andreas fault from an original position. It is predominantly Mesozoic granitic and pre-Cretaceous metamorphic rock. There is some Cretaceous sedimentary rock of the Great Valley Sequence, considerable Miocene marine sediments, and some other Tertiary sediments. Units west of the Sur-Nacimiento fault are dominated by rocks of the Franciscan Assemblage.

-Identified to be of igneous origin

-Phaneritic in texture

-Large crystal structure

-Felsic composition

-Intrusive (because of the coarse-grained texture).

-presumed to be light in silicates as granite contains only 10% dark silicates.

Identified to be of

metamorphic origin.

white with reddish/pinkish

stains.

Non-foliated/Porphyritic

texture

Medium-coarse grain

Felsic composition

Parent rock-Quartz sandstone

Identified as Igneous

in origin

Looks to be

Pyroclastic in texture

Intrusive (coarse

grain)

Pink/reddish in color

Mafic (Basaltic)/Gabbro

composition

Much of the outlying rock families in this

immediate area seem to be very consistent with

the Metamorphic/Igneous families.

A solid amount of this area does contain

sediment and sedimentary rock.

Most of my findings and rock samples are not

consistent with the sedimentary history that is

suggested through out this area.

Perhaps Metamorphism and the metamorphic

rock cyclic processes has taken over within this

area over the past century or longer.

by: Jean Reyes

Located in central

San Luis Obispo

County

Flows parallel to the

Santa Lucia Mountains

Elevation-2,400 ft

Mouth-Monterey Bay

Length-175 Miles (282

km)

Basin-4,160 sq miles

Because of its periodic dry

climate and dry river bottom

at times during the summer,

the Salinas river bed endures

harsh erosion.

During the summer months

the Salinas river dries up. In

the winter, during rain and

flood seasons, heavy water

and strong currents break

down the river bottom.

-this picture shows a prime

example of erosion and the

weathering process that

occurs.

Built and developed

during WW2 to

transport troops to

and from Camp

Roberts Military

Training Center.

Operated by Southern

Pacific Railroad

Transport

No longer in operation

(derailed after the

Korean war)

Nacimiento River Dam

was constructed in

1961.

Built by the Monterey

County Water Authority

for flood control and

water irrigation.

Created Lake

Nacimiento which is

now used by people for

recreational purposes.

It is a 210 ft earth fill

dam.

Nacimiento Nacimiento Dam

Spillway has been

undergoing extensive

repair and modification

operations since 2008.

Purpose of

modifications is to

ensure safety

regulations and to

improve release

maneuvers incase of

large floods.