Welcome to theWelcome to theWelcome to theWelcome to theWelcome to theNarrows Earth Trail!Narrows Earth Trail!Narrows Earth Trail!Narrows Earth Trail!Narrows Earth Trail!

Faulting, flooding, gravity and wind aresculpting the earth. The story is written inthe rocks. Its a story thats been writtenover millions of years and is still being writ-ten today. We humans are visitors duringonly a brief span of time.

Follow the numbered posts for a trip intothe exciting and moving world of geology.

1. Ancient Granite1. Ancient Granite1. Ancient Granite1. Ancient Granite1. Ancient GraniteMore than 100 million years ago, this rockin front of you began to form deep insidethe earth. It was hot liquid rock, calledmagma. Thrusting into the earths crust, itslowly cooled underground and hardenedinto igneous rock. Because it cooledslowly, it crystalized into a variety of min-erals, giving it a speckled appearance.

It took millions of years of weather and ero-sion to expose this type of igneous rockcalled granite thats so noticeable in Anza-Borrego Desert State Park. Long ago, thesand youre standing on was part of therocky hillside around you. From magma togranite to sand to what next?

If you could stay for a few thousand years,you might see it form into layered, or sedi-mentary, rock. Over time, the sedimentarylayers could be pushed up to create newhills around us.

2. Earth on the Move2. Earth on the Move2. Earth on the Move2. Earth on the Move2. Earth on the MoveThe concrete and boulder wall in front ofyou was built by the road crews back in the1930s. The crews named this area Pow-der Dump Wash. It was part of a storagehouse where they kept explosives.

rounded by many large and active faults thatwe share with folks all over the southwest.

Northeast of us is the San Jacinto FaultZone. Towards the west-southwest is theElsinore Fault Zone. Both of these majorfault zones are associated with the San An-dreas Fault, the largest and one of the mostactive in California.

Geologists studying the San Andreas Faulthave discovered identical rock material oneach side of the fault, 400 miles apart. ThePacific Plate continues to move north, car-rying local rock with it as it travels. If yousit on a coastal rock in Monterey, yourelikely sitting on a rock that was once hereat Anza-Borrego.

If you look upslope from it, youll see wheretwo different types of land meet. The dis-tinct line where the two rock types cometogether is called a contact zone.

This contact zone shows us that there is afault line here. Notice how the rock edgesare worn along the contact zone from theforce of constant movement? Imagine thetremendous power that slams these giantwalls of bedrock together during an earth-quake.

Speaking of constant movement, have youfelt the earth move? Dozens of tiny quakesshake this area daily.

3. Hard Rock, Soft Rock3. Hard Rock, Soft Rock3. Hard Rock, Soft Rock3. Hard Rock, Soft Rock3. Hard Rock, Soft RockLook up to your right at the small cavesand holes in the sedimentary rock. Whenthis rock was formed, it had pockets ofsofter material here and there. Over time,rain and wind removed the softer rock, leav-ing the tiny caves.

Most of the slopes of the Vallecito Moun-tains above you consist of granitic rockpushed up fairly recently from inside theearth. Because youre in an area fracturedby earthquake faults, youll see older sedi-mentary rock right next to granitic rock.Watch for examples of this and more holeyrocks along the trail.

4. Faults Everywhere4. Faults Everywhere4. Faults Everywhere4. Faults Everywhere4. Faults EverywhereDo you see the crack in the rock wall infront of you? You probably already recog-nize it as a fault. The rounded edges of thecontact zone and the different kinds of rockmaterial on each side give it away.

Here at Anza-Borrego there are thousandsof small faults like this one. Youre also sur-

Narrowsearth

Nature Trail Guide

California State Parks

2003

Come take a peek at Anza-

Borregos geological story

along this short, easy trail

the Narrows Earth Trail in

Powder Dump Wash.

By the way, faults are the main reason Anza-Borrego has its wonderful palm oases. Thefault line creates a crack in the earth thatallows water to seep up. In this region thereare hot springs and cold springs.

5. Salt and PepperAlong the trail you may have seen darkercolored rocks. These darker rocks wereformed over thousands of years when thisarea was covered by an ocean.

These sedimentary deposits have beenmoved aside by the harder granitic rockthats pushing up through it. Its calledtonolite and is a mixture of feldspar, thesalt in the granite, and mica, the pepper.

6. Time warpDoes this rock look different? Youve justgone back in time. Some of the oldest rockin Anza-Borrego Desert State Park standsin front of you.

This rock was created when forces com-pressed and warped mud and sand layers.Its a good example of metamorphic rock,that is, rock thats been changed by pres-sure, heat or chemical action.

When this rock was at the bottom of thesea, about 450 million years ago, this cliffwas located south of what we now callGuaymas, Mexico.

On the left side of this formation,notice howthe layers of sedimentary rock are turnedvertical by natures forces.

Behind you is a dark streak in the hillsidejust like the one youre facing. Water, rac-ing down the mountain, cut a wash rightthrough the middle of this formation.

7. Water works7. Water works7. Water works7. Water works7. Water worksLook back up into Powder Dump Wash tosee the rugged slopes of the mountain. Sum-mer thunderstorms drop heavy rain thatcarries enormous loads of sand and graveldown. This sloping land in front of a moun-tain is called an alluvial fan.

This alluvial fan leads into San Felipe Wash,which, during torrential summer storms,carries water all the way to the Salton Sea,25 miles away.

As you prepare to leave Powder DumpWash, notice the white streaks of quartz onthe walls of the Narrows. The next wash tothe east is Quartz Vein Wash, named afterthe beautiful streaking in the dark walls.

Our lifetimes are but a blink in the eye ofgeologic time. Faulting, flooding, gravity andwind continue to sculpt the earth.

Here, the story is written in the rocks.Where you live, the evidence may be lessvisible. But wherever you are on Earth,youre surrounded by the active processesof geology.

We hope youll look for the stories writtenon the land as you travel through the restof the park and back home again.