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FrontRangeLiving.com -> Garden -> Geologist's Garden
 WHEN
ROCKS TELL HALF THE STORY: A GEOLOGIST'S GARDEN
By Niki Hayden
Cathy and Bob Eppinger faced the usual dilemma in a mountain home after
excavating a garage. An unsightly heap of stones and dirt proved too expensive
to haul away. Why not turn that mound of rock and grit into a garden? With Cathy
as the gardener and Bob as a builder of the rock wall, a problem turned into a
triumph. Along the way, Bob discovered that his rocks told a geological story
that most people would not recognize.
As a research geologist for the U.S. Geological Survey, rocks are his passion
as well as vocation. Small rocks collected from around the world line up along
his property like a photo album, all memories of his travels.
 When it came to assembling a wall, rock after rock reminded him of the
ancient history of Colorado--when mountains formed, rivers eroded sandstone and
giant planes of rocks uplifted along the Front Range. By the time he finished
his wall, the serpentine line read like a time line of stresses, fractures,
upheavals, and erosion. Each few feet of wall revealed an era from the past, a
visual frieze that defines a sliver of Colorado.
As he walks alongside the wall, Bob begins the story from the most recent
past, with sandstone--the elegant, soft red Lyons sandstone that is cut from
quarries and makes up the buildings on the campus of the University of Colorado
at Boulder. Sandstone is sedimentary stone, a sandwich of sand and clay.
"That’s the youngest rock," he says, "it’s actually petrified
dunes, windblown and ranges from about 240 to 290 million years old."
The sandstone is almost crumbly. It’s beautiful when stacked together and
the stacking increases durability and strength. Sedimentary is one of three
categories of rocks that make up the world. A more durable rock is igneous, a
molten rock that includes granite. The third is metamorphic, a composite of heat
and pressure that forms crystals, which explains a rock like gneiss. Although
the science of geology is vast and complex, these three groups of rock both
explain and define how the earth’s surface was formed through heat, pressure,
water and wind.
 Along Bob’s wall, after the Lyons sandstone comes the Fountain Formation,
which makes up the Boulder Flatirons, the Red Rocks of Morrison, and the Garden
of the Gods in Manitou Springs. "About 290 to
310 millions year old," he says, which places it older than the sandstone,
but still a porous, red rock rounded by erosion and a "signature of an
ancient mountain range that was completely eroded away and eventually replaced
by the present Front Range."
As Bob built the wall, hoisting rock after rock into place, Cathy planned the
garden. At 8400 feet in altitude, she battled late snow showers in June and
early frosts in August. Most difficult, though, was not the weather, but the
gophers. Before filling any gardens with soil, she decided to try layering
chicken wire at the bottom of each large rock cavity so that small, voracious
critters couldn’t dig from the base of the garden. So far, she says the wire
has worked.
Through trial and error, Cathy planted perennials that she believed would
thrive in her climate. First she put in iris and poppies from her parent’s
garden. Then went in columbines. They’ve self-seeded over the years and bounce
back from chilly weather. Creeping phlox and basket of gold are mountain plants
that long ago adapted to high altitude gardening. Delphiniums and Shasta daisies
could be smashed by late snows, she acknowledges, but they proved to be
predictable bloomers arriving just in time for late spring.
 Bob’s wall
continues, moving back in time to what he calls, "Precambrian granitic
rocks of the Boulder Creek Granodiorite, 1.7 billion years old." In the mid-section of the wall are the fine, very
dense rocks that would contain gold and silver, iron and tungsten. "We’re
in the very old rock," he says, "it’s a huge body of rock
called batholith that covers much of the mountainous area of Boulder
County. One particular rock is a feature of the mountain cross section. The Iron
Dike as it is known locally by geologists is a significant structure in the area
descending from Rocky Mountain National park southeast to the Magnolia area. A
dark rock and very heavy, the Iron Dike is about 1,300 million years old and
cuts the lighter gray granitic rocks in the wall."
"Lighter-colored quartz-rich igneous rocks represent the magnolia mining
district where gold telluride deposits were mined from the late 1800s into the
early 20th century. Tungsten was found at Magnolia. These are the mountains that
would attract miners and speculators with veins of riches. The mineral deposits
are of Tertiary age, forming at a much later date, less than 60 million years
ago. During its heyday, many hundreds of people lived and worked at the old
mountain town of Magnolia," he says.
But he also found quartz stones when his garage was built, beautiful white
rock with veins of reds and purples.  "These are quartz veins with a lot of
iron and manganese in them," he says. "The veined and fractured rocks
are consequences of heating and rapid pressure release, creating rocks called
breccias."
Cathy set about mixing the original mountain soil with potting soil and
compost. "We can’t compost here because of the bears," she says. A
worm farm in the basement provided castings for the garden soil. Instead of
tinkering with seeds, Cathy decided to buy healthy potted plants. The growing
season is too short in the mountains to start out with anything less, she says.
Even bare rootstock was dismissed. "Then I began to experiment each
year," she says, "I’ve now got currants and rhubarb. And while I
have planted sweet peas from seed, they don’t carry over from year to
year."
 The wall snakes along with more granite, iron and quartz. At the end, the
rocks take on an orange tinge. "They were closest to the surface," Bob
says, "so exposure to oxygenated groundwater has changed their color from
gray to hues of orange." The wall ends with gneiss, a metamorphic rock of
the Idaho Springs Formation and the oldest rock at 1.8 billion years old. "At
great depths, the granite pushed its way upward into the gneiss. Very recently
on the geologic time scale, all the overlying rock has been uplifted and
stripped away by erosion and there are only residual islands of gneiss left.
These remnants are called xenoliths. They
are a neat feature, that’s why I wanted them in the rock wall," he says.
If you took a vertical slice through the rocks from the mouth of Boulder Canyon up
Magnolia Road and toward the town of Pinecliffe, the rocks would look somewhat
like Bob’s wall. 
And while rock formations differ across Colorado, the
exposed layers of sandstone, granite, quartz and gneiss create a dramatic
natural theater.
As spectacular as a mountain setting may be, Cathy says it doesn’t provide
ready access to water. She depends on a well or catching rainwater and snow, so
her garden has to get by on as little water as possible. A sprinkler system
delivers water when needed but many of her plants, well mulched, get by on
little. Partly the cooler temperatures at high altitude cut down on
transpiration. Also, she has weeded out plants that clamor for too much water.
"Shasta daisies droop a bit when they need water," she notes, but
they, too have to suffer through truly dry spells.
"I tried to mix the blooming to have flowers all season," Cathy
says, with the early flush of phlox and columbines followed by delphiniums and
daisies. Many, like the columbines she allows to reseed and several plants of
bleeding hearts, have thrived. If a plant needs more protection, she may move it
from the rock garden to sheltered gardens on another side of the house.
Raspberries survived best when moved from a sunny east to a more sheltered west
side of her home.
 The wall ends with xenolith formations, remnants of gneiss, topping the rock
wall. Bob says he placed them on top as nature positioned them. "The gneiss
is a metamorphic rock whose remnants appear to be floating in the formerly
molten granite. Then rock all around it eroded away," he says, which provided
a spectacle for tourists millions upon millions of years later.
Bob and Cathy’s garden may be a joint venture between gardener and mason,
but it’s also a hallmark of the essentials in rock gardening. The combination
of ancient rocks and ephemeral beauty defines much of mountain gardening in the
West. Poppies and delphiniums remind us that summer is brief at high altitude,
to be savored all the more. But for an all season garden, rocks, of course, last
forever and provide a stunning backdrop all along the Front Range in every month
of the year.
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