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Gems Just A Stone's Throw Away : Hunting Hard Rocks, Golden Opportunities

July 11, 1991|BRIAN ALEXANDER

For proof that fun and education are not oxymoronic, look at your feet. Better yet, go outside and look at your feet.

There's a good chance you will be standing on some sort of mineral, a mineral that can tell you a lot about the planet on which you live, a mineral that may even be able to make you a little extra money.

San Diego's North County is a gold mine of minerals. Even after more than 100 years of commercial mining and the development booms that have left little land available for prospecting or rock hounding, there is still plenty to see and collect. In the process you may learn a lot about San Diego history and science.

Let's go back a ways. A few hundred million years ago California was undergoing some changes that made it the treasure trove it is today. Back when the earth's plates began sliding past each other, the state was literally part of Mexico, sunning itself down around Sonora. As the state moved north, it took along rocks that had been left by streams originating in inland Mexico. It also took with it a 300-mile-long ridge of coarse granite now known as the Southern California Batholith.

Large deposits of pegmatite are found along this ridge. As the crust of the earth changed, minerals were dissolved and then precipitated back out of the water and gasses. They formed crystals. Depending on the mineral involved, those crystals became tourmaline, garnet and a host of other crystal forms. Most of these crystals are found near pegmatite.

Gold was also deposited throughout California. San Diego received a good deal of the deposits, enough to spawn a few minor gold rushes.

If all this seems a bit much for the average person who doesn't know if breccia is a pasta or a rock (it's a rock), don't panic. You don't need to know much about rocks in order to enjoy looking for them.

ROCK HOUNDING

It's no longer easy to find a good rock in San Diego County, says Frank Knechtel. The 74-year-old Knechtel is a member of the San Diego Mineral and Gem Society and something of a historian on local rock hounding.

"You go back to where you used to collect 20 years ago and there's a house on it," said Knechtel. "I gave up field collecting around here because there's not anything left."

Collecting isn't exactly a thing of the past, though.

According to Will Estavillo, curator of minerals for the San Diego Natural History Museum, development has greatly diminished the number of places for good rock hunting, but there are still a few left.

The easiest spot to look for rocks is the beach. That's the bright spot in the increasing rockiness of our shores. Because inland streams have been dammed, and because the drought further restricts the flow of water toward the coast, beach sand is not replenished and the sand already on the beaches is swept south by wave action.

But although your feet may curse the stones that stay on the beach, your eyes can be treated to a tremendous variety of interesting, and sometimes semi-precious, rocks. According to Estavillo, these are the stones brought to the county from Mexico so long ago. Some, like 1.5 billion-year-old quartzite, are among the oldest rocks on the continent. Others are young. Granite is a newcomer at 60 million years old.

Estavillo used to make a living collecting beach rocks. He carved them up into jewelry and sold them at art fairs. Even now, watching him pick over rocks at the beach is like watching a baseball card collector in a room full of Mickey Mantle rookie cards.

The beaches contain at least half a dozen semi-precious forms of rock like jasper, agate, moonstone, quartz, gold (a metal), and garnet. Sometimes it is possible to find tiny diamonds among the sparkles.

Because the rocks will have been naturally tumbled in streams and by the waves, they will appear dull on the outside. Try looking for them at the water's edge. Wet rocks seem more lustrous and the good ones are easier to see. When you have found a few nice specimens, you can take them home and slice them open with a diamond saw to reveal the real treasure. A little spray lacquer will keep the rocks looking wet.

Lapidary classes such as those given by the San Diego Mineral and Gem Society will teach you how to make jewelry from your new finds.

Any beach that has become cobbled is a good hunting ground. Estavillo likes the beach about a mile south of the Encina Power Plant at Carlsbad. Other cobbled beaches include Beacon's at the foot of Leucadia Boulevard.

Rock hounding inland is only slightly more complex. You'll need a magnifying glass, a geologist's pick, a spray bottle of water (to make potential finds shiny), and lunch.

While much of North County is now off-limits, Estavillo thinks the weekend hunter has at least a few options.

The first is road cuts, those spots where a hill has been gouged to make way for pavement. These areas allow you to see a good cross-section of the hill. Just pull well off the road and start looking.

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