Sinkhole near East Remote Parking Lot. Photo courtesy of UCSC Environmental Studies Department.

Imagine a building site with a multimillion dollar project in full swing and suddenly the concrete for its foundation starts to disappear into a dark sinkhole with depths unknown. Sound like a rare occurrence? Not entirely. While this an extreme, though true case, sinkholes have wreaked havoc in greater or lesser degrees on seven buildings on the University of California Santa Cruz (UCSC) campus.

Sinkhole-filled topography underlies the UCSC campus. It is called “karst topography” and is created when limestone/or marble bedrock dissolves for many thousands of years and leaves deep holes, winding tunnels and narrow fractures. The reaction between acidic groundwater and the underground lime causes the rock to dissolve into the ground water and simply flow away. A swiss cheese pattern is created underground with holes ranging from tiny to huge and cavernous. This geologic phenomenon has allowed many-a-student to have fun in the caves but also proves quite challenging when it comes to constructing large buildings.

I recently had the opportunity to speak with Dr. Gerald (Jerry) Weber about the karst geology of the UCSC campus. He has served as a local planning advisor, taught the UCSC summer geology field camp for 20 years, and has been investigating geologic problems in California for about 50 years. Jerry’s services are used when sinkholes threaten building projects on campus and he has some great stories to tell.

Sink Hole Spotting

The UCSC campus is peppered with sinkholes only noticed by the trained eye. The 50 plus sinkholes on campus are the most noticeable characteristics of the underlying karst topography. When caves grow so large that the weight of the ceiling material is no longer supported, it collapses; thereby creating a sinkhole (doline). Other ways that sinkholes are created are from a settling of surface material over highly fractured dissolving marble or the sinking of soil that has filled widened cracks in marble below.

Map of sinkholes and fracture/fault zones on campus. Photo courtesy of the UCSC Environmental Studies Department.

The sinkholes leave the imagination to wonder to what depths these caves reach. Geologists conducted a 200 foot core sample and still haven’t a clue of the extent of the karst cavities. At first, the UCSC campus terrain seems solid and continuous. Images of rolling grassy hills and massive redwoods disguise the deep voids that could be just 15 to 30 feet below the soil surface.

In front of the Baskin Engineering building, hidden beneath the shade of redwoods, lies a large sinkhole. Photo courtesy of Lauren McEvoy.

It’s San Andreas’ Fault

Most people know of the San Andreas Fault that runs almost the length of California but not many are aware of the 33 plus fracture zones and faults that are spread across the UCSC campus. Disguised as dry creek beds, Chancellor Gulch and Jordan Gulch are the largest fracture/fault zones on campus running nearly the entire length of the campus. Movement along these faults creates areas that are pulverized and more permeable. These porous areas make the perfect outlet for groundwater flow in the rainy season and create underground rivers with no destination in sight. Most of the creeks on campus will appear from springs up river and then disappear underground into a closed sinkhole (swallow hole) into the deep unknown.

Karst topography at its full extent. Photo from the collection of Jerry Weber.

Where does the Water Go?

No one really knows where all the water goes. Geologists in 1989 drilled wells into the fault/fracture zones to test the amount of stored water. They have found huge water rich aquifers within the karst producing up to 200-300 gallons per minute with little drop in the water table. Despite the sheer amount of water stored right under campus, the city supplies the campus with water for reasons that mystify me in my investigations. Water in karst systems has a high potential for containing contaminants due to lack of filtering (percolating) before reaching an aquifer. Most drinkable water from aquifers has been filled with water that has filtered through layers of clay and other cleansing particles. Instead, the water in karst systems go from cloud, to ground, to storage system much more quickly and with less natural filtration.

Building on Karst

Avoiding underground caverns is challenging when planning for development. Before building on campus is approved, extensive geologic and geotechnical engineering studies are done to gauge the strength of the underlying bedrock. Exploratory drilling to sample the bedrock for voids is done for every major building project on campus. Voids were found before and during construction of eight known structures at UCSC and the weight of a few of these buildings proved too much for the underlying karst.

Prior to the construction of the Science and Engineering Library a large narrow void filled with a toothpaste consistency clay material was discovered at the exact location of the planned library. Construction began after coming to realization that the only way of building over such terrain was to construct an underground bridge spanning the river of clay. Hundreds of students use the library daily without a clue that a river of mud lies just below the foundation of the building.

Thirty boreholes were done to understand the geology under the Science and Engineering library prior to construction. Photo courtesy of Lauren McEvoy.

There is a very large sinkhole in front of the Baskin Engineering building that gives a clue as to what lies beneath the adjacent building. Baskin Engineering was constructed atop a very deep cavern with unknown depths. When construction began the void was discovered and filled with an enormous amount of cement day after day until workers realized that the hole was not being filled at all. Their efforts to fill the hole failed. Instead, cement pillars 300 feet in length were placed deep into the earth in stable bedrock surrounding the void. Its as if Baskin is hanging over the mouth of a hungry giant.

Baskin Engineering straddles a big karst cavern. Photo courtesy of Lauren McEvoy

After the construction of the Earth and Marine Building foundation, the weight of the cement foundation proved too much for the hole-filled karst below. In December 1991, just weeks after completion of the foundation, an enormous rain storm whipped through the campus over the New Years Holiday. Construction workers came back from their holiday to discover that their hard work had fallen victim to the inevitability of the karst topography and rainwater combination.

The foundation had given way and collapsed into an underlying cavern. Geologist, Jerry Weber, stuck a 30 foot rebar into one of the open holes and couldn’t feel the bottom of the cavern. Construction workers pumped cement into the exposed holes until the foundation was stable enough to prevent the cavern from eating any more of the building.

Earth and Marine Sciences Building. If its not tree sitters, its sinkholes that are trying to stop development on campus. Photo courtesy of Lauren McEvoy

Geek Details: Chemistry of the Karst

Rainwater lands on the campus soil where it flows and accumulates tiny dissolved acids and carbon dioxide gas. Groundwater becomes slightly acidic when the carbon dioxide dissolves, producing carbonic acid.

carbon dioxide (CO2) + water (H2O) = carbonic acid (H2CO3)

When the acidic groundwater finally reaches the marble bedrock (cooked limestone), it finds its way into tiny cracks, joints and fault lines. As carbonic acid laced rainwater drizzles through these cracks, the lime within the marble dissolves. 97% of marble on campus is composed of lime which means that the lime loving carbonic acid has potential to drastically change the structure of underground topography by dissolving a large percentage of the marble.

lime (CaCO3) + carbonic acid (H2CO3) = calcium ion (Ca++) + bicarbonate ion (2HCO-3)

Sinkholes can be formed many ways. Photo courtesy of the UCSC Environmental Studies Department.

Over time, these tiny permeable cracks enlarge and create tunnels and caves large enough to throw a party in. Despite the severe effect that acidic water has on lime, it is not a risk to humans. It only affects the geology so greatly because it has been working at dissolving lime for the past several hundreds of thousands of years (on a geologic timescale).

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This piece is part of the UCSC Natural History Tour. Download the free app with many tours of the Santa Cruz area and beyond.

A young woman sits among a cathedral of redwood trees in Henry Cowell State Park, circa 1903. Photo Courtesy of California Historical Society Collection, 1860-1960.

Tucked away in the mountains of Santa Cruz, adjacent to the UCSC campus, is a hidden treasure called Pogonip. One step into this hideaway will bring to light the sedateness of Pogonip contrasting the hustle and bustle of the city just a few miles south east. The large mossy lime kilns, unforgettable tall redwoods, warm sunny meadows and an interestingly placed koi pond make Pogonip a destination worthy of being at the top of bucket lists worldwide.

Lime stone kilns still remain at Pogonip as a reminder of past uses of land. Photo © Lauren McEvoy.

Lime Kilns

Abandoned fern covered lime kilns riddle the land that make up Pogonip and the UCSC campus. In the early 1800s lime kiln companies in Santa Cruz viciously fought for business to sell to the leading buyer of lime for construction in San Francisco. Laborers worked tirelessly to haul and load lime rock into kilns by continuously adding wood to the fire that heats and separates lime (calcium carbonate) from the mined limestone.The fires that blazed within the walls of the kilns were fueled by Douglas-fir and redwood logged from the surrounding forest.

Lime from Santa Cruz was of the finest quality and was largely used in San Francisco for “hard finishing” walls (plastering and smoothing out lumps and bumps during construction of walls). Lime from Santa Cruz helped build young San Francisco from a modest sized town to a vast world renowned city.

Logging in the Santa Cruz mountains, circa 1900. Photo courtesy of California Historical Society Collection, 1860-1960.

When hiking or viewing current photos of Pogonip, it looks as though nature has reclaimed the kilns. Ferns and mosses shroud the walls of the kilns camouflaging them into the surrounding regenerating forest. Blankets of under story plants and healthy forests of redwoods and Douglas-fir now cloak the land. Without prior knowledge, it is hard to imagine the sheer amount of labor, logging and competition that took place at Pogonip just over 100 years ago.

From Rocks As Revenue to Rocks as Art

Rock art in a rock oasis.
Photo © Lauren McEvoy

Fast forward to the 21st century and people are using the local rocks for art instead of commerce. A small trail that leads behind the two lime kilns off of Rincon Trail passes a secret oasis of rock art. Students regularly go here to retreat from school between classes to meditate, relax and think. There are hundreds of rock towers performing crazy balancing acts.

Within nooks and crannies of some of these rock towers are notes left by students. Some are words of encouragement, riddles to be solved and some share the challenges of attending a progressive school.

Progressive schools mean more hiking. Photo © Lauren McEvoy.

Koi, Tufa and Redwoods

Of the many trails at Pogonip, Springbox Trail is exceptionally prized. From Rincon Trail take the short but sweet Springbox trail which leads the explorer to a rare sight. A spring that trickles cold clear water from a deep aquifer surfaces just a few steps from the entrance of the trail. It flows down a rugged sandstone creek bed coated with tufa (pronounced TOOf-a). Down it flows passing tropical plants that UCSC students have planted. The water then flows over the roots of a tall redwood tree benefiting from this constant supply of fresh cool water.

This small spring box catches the initial flow of the spring. Photo © Lauren McEvoy

Finally the flow comes to a glassy halt as it swirls into a square pool filled with Koi and goldfish that students and locals have replenished when their populations dwindle. It is highly frowned upon but in the heat of summer students have been known to go for a skinny dip.

The spring box is also lined with tufa. It resembles a veneer of creamy brown butter spread on every surface. Tufa is a soft porous type of limestone produced when calcium carbonate precipitates out of water that has surfaced from deep aquifers rich in lime like those around Pogonip and campus. The tufa even precipitates on twigs and leaves. In some cases, tufa has enveloped twigs that later decompose and leave tiny craters and tunnels within the tufa.

The beautiful Koi pond at Pogonip is a favorite destination. Photo courtesy of Alex Darocy.

About 50 feet south of this tufa encrusted paradise is a tall knobby old growth redwood tree. It stands facing the ocean surrounded by second growth giants. Because of its odd look, it is only one of the few old growth redwood trees spared during the height of the logging era.

Take the Self-Guided Mobile Tour

This piece is part of the UCSC Natural History Tour. Download the free app with many tours of the Santa Cruz area and beyond.

1. Sources Used

   • Tonya Haff, Martha T. Brown, W. Breck Tyler (Eds.). The Natural History of the UC Santa Cruz Campus, Second Edition. Environmental Studies Department, University of California, Santa Cruz. 2008. [Review]
   • Joan Gilbert Martin and Colleen McInerney-Meagher. Pogonip: Jewel of Santa Cruz. Santa Cruz, CA: Otter B, 2007. [Review]
   • Frank Perry. Lime Kiln Legacies: The History of the Lime Industry in Santa Cruz County. Santa Cruz, CA: Museum of Art & History, 2007.
   • Who Was Henry Cowell? California State Parks Website.
   • The Pogonip. Santa Cruz Public Libraries.
   • The Pogonip. Hilltromper.
   • The Pogonip. LocalWiki.
   • Pogonip Clubhouse. Deep Blue Moon Website.
   • Guide to the Pogonip Collection. Santa Cruz Museum of Art and History Website.

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A beautiful honeysuckle hill on the way to the Lost Boys house. Photo © Lauren McEvoy

On the University of California, Santa Cruz Campus, east of Stevenson College and across Coolidge Road, you will find one of the seven entrances to Santa Cruz’s beloved open space preserve, the Pogonip. With 640 acres and 8 miles of trails, the Pogonip is a favorite place for locals to connect with nature. Inside, dark mystical redwood forests with light dappled understory give way to oak woodland habitat that open onto warm sunlit grasslands comparable to scenes from “Little House on the Prairie.” The challenge is to decide where to linger.

View from Prairie Hill. Photo © Lauren McEvoy

Cowell Family Estate

The UC Santa Cruz campus and much of the Pogonip land was originally part of Cowell Ranch. Henry Cowell bought the land in 1865 for its extensive lime and timber resources. Cowell and his family owned the Pogonip portion until 1989 when the Cowell estate sold it to the City of Santa Cruz. The Cowell estate has their name stamped on some of Santa Cruz’s most beloved retreats left to public good. Besides Cowell College on the UCSC campus, the Cowell family name can be found on Cowell Beach next to the Boardwalk, and Henry Cowell State Park in the Santa Cruz Mountains, all due to land gifted to the public by the Cowell family.

The Pogonip Clubhouse

In the heart of Pogonip lies a dilapidated building with peeling paint that is rich in history. In the early 1900s, it was called the Casa Del Ray Club and Golf Links, or the Pogonip Clubhouse. It was a hot spot for the surrounding golf course at Pogonip. People would come far and wide to play at the spectacularly beautiful golfing spot.

Casa Del Ray clubhouse circa 1900. Photo courtesy of the Santa Cruz Museum of Art and History.

In the 1930s, Dorothy Demming Wheeler revamped the golf links into polo fields that soon became a haven for talented women polo players. She called the new and improved clubhouse the Pogonip Polo Club. Wheeler helped break a long standing barrier for women in sports. The clubhouse was closed during World War II and was used as a rehabilitation facility for wounded soldiers. In 1948 the clubhouse reopened for use as a social club before the City of Santa Cruz bought it in 1989.

Golf players flock to the beautiful golf club at Pogonip, circa 1900. Photo courtesy of the Santa Cruz Museum of Art and History.

The clubhouse was used as a set for three movies, including one teenage vampire movie that trumps all modern day teenage vampire movies: “The Lost Boys”. There are free showings of this action packed thriller on Main Beach in the summer projected on a giant screen. Heart throb (in 1987 of course) Corey Feldman who played one of the leading roles occasionally attends these showings.

At first sight the once hopping clubhouse looks as though it may collapse from even a mere sneeze. There’s now a six foot wire fence barricading the building from the interested tourist and the party spot seeking UCSC student.

The front lawn of the Pogonip Clubhouse is a great place to have a picnic. Photo © Lauren McEvoy

A Pogonip Haunting

Near the northern section of Pogonip, the ghost of Henry Cowell’s daughter, Sarah Cowell, is said to drift among what locals call the Haunted Meadow. In 1903 the local paper touched on the story of Sarah Cowell and Evelyn George, the wife of the Cowell Ranch manager. They were apparently thrown from their horse-drawn carriage while returning to the ranch. Mrs. George was severely injured but survived. Sarah Cowell died after repeated, desperate attempts to revive her.

The Haunted Meadow does not look so haunted in midday. Photo courtesy Lauren McEvoy

Some say her ghost haunts the meadow in the darkness of the night. She is seen only as a long white cloak hovering above a shadow below the moon light. Only the bravest of souls should explore the haunted meadow in search of Sarah Cowell. The story of Sarah Cowell’s death has transformed over time and despite the ghostly stories at Pogonip, her accident actually occurred “near Cowell’s upper kilns” which is now a part of Wilder Ranch State Park. Despite the true location of the accident, maybe Sarah’s ghost visits the Haunted Meadow anyway.

Visiting the Pogonip

The Pogonip is a captivating gem loved by Santa Cruzans and visitors alike. Visitors should be aware that on-site parking, drinking water and toilets are non-existent. Before heading out, be sure you know what poison oak looks like, as it can cause a itchy, angry rash!

Poison oak leaves an unforgettable rash. This lobed leaf can be in colors of green and red. Photo courtesy :Elf

Beyond connections to nature, north of Fern Trail another connection has permeated the forest. Word on the street is that drug dealers linger in those neck of the woods so steer clear of anyone who doesn’t look like a hiker, biker or park worker.

Take the Self-Guided Mobile Tour

This piece is part of the UCSC Natural History Tour. Download the free app with many tours of the Santa Cruz area and beyond.

Empire Cave, also known as Porter Cave. Photo © Lauren McEvoy.

Located near the west entrance to UC Santa Cruz, Cave Gulch has many charms. The majestic redwoods are the most obvious one and they set the stage. Their thick tall trunks, earthy smell and drooping boughs play with the sunlight and create a feel of enchantment. I often feel that a forest sprite might jump out at any moment. Read on as many of the unique treasures of Cave Gulch are revealed.

Karst Caves

There are many caves on the UCSC campus and most are along Cave Gulch (hence the name). The caves exists because of a Swiss cheese like nature of the bedrock beneath your feet – its called “karst” topography and it exists where you have rocks made of marble (basically cooked seashells) that have interacted with water. Over millions of years, slightly acidic ground water dissolves the calcium carbonate (CaCo3) from marble bedrock and creates deep fractures and holes. Over time the fractures can enlarge and create tunnels and sometimes really large spaces known, of course, as caves. The caves tend to form along fault zones, because the physical grinding along the fault makes it much easier for water to penetrate and start the process of dissolving the marble (chemical erosion). It turns out Cave Gulch has a a fault right in the areas where most of the caves are, in fact, the trace of the fault pretty much defines where the creek runs. So the famous HellHole and Porter Caves of UCSC partying lore exist thanks to faults moving within the larger San Andreas Fault System.

Down into the depths of Empire Cave. Picture © Lauren McEvoy

Stalactites and stalagmites used to be common in the caves but most have been destroyed or taken away by the curious. A few remain but if I told you where they were the forest sprites would smite me. The caves can be very dangerous especially in the rainy season. Rule of thumb: when it’s moist outside, it’s wet and slippery inside the caves. If you choose to explore please do so carefully, respectfully and responsibly.

Warning sign at the entrance of Cave Gulch. Photo © Lauren McEvoy.

If you’re visiting Cave Gulch in winter in a wet year you might see water flowing in the river bed. The bedrock in some places is not marble but made of metamorphosed (cooked) sediments called schist and granite. Unlike the fractured marble, they hold the water more like a canal. At some points the flow in the river abruptly disappears underground; this is where the schist or granite has hit a patch of marble rattled with cracks, holes and tunnels.

When lacking flow, this water-less river bed creates an opportunity for artists to create rock balancing art. Photo © Lauren McEvoy

Drinking up the Fog

The tall Redwoods are very thirsty and require a lot of water, up to 130 gallons per day for the average tree. They survive our Mediterranean dry summers and droughts by harvesting fog-water with their leaves. Some of the water is absorbed through their leaves but most falls to the forest floor where their roots and other understory plants can drink it up. This availability of water to the forest floor is why redwood forests stay vibrantly green even throughout dry summer months.

The Forest Floor

Below the Redwood trees you’ll see many comparably smaller plants blanketing the forest floor. Clusters of ferns big and small scatter mosaically among the landscape of Cave Gulch. Wet mats of bright green moss cover rocks and tree trunks resembling scenes from “The Lord Of The Rings”. One of my favorite ground covers is Redwood Sorrel because it gives the imagination that fairies and hobbits could be living among the forest leaf litter.

Redwood Sorrel Oxalis oregana. Photo couresy of Lauren McEvoy.

In early spring, look out for the delicate Fetid Adder’s Tongue that smells of decayed mushrooms. Their undeniable beauty among the darkness of the Redwood forest would never indicate its offensive smell.

Fetid Adder’s Tongue Scoliopus bigelovii. Photo © Lauren McEvoy.

Critters On The Ground

One animal you can find year round is UCSC’s Mascot, the slimy Santa Cruz Banana Slug. They may look like a fallen yellowed Bay leaf but look closer and you will see four tentacles guiding a ripe banana peel colored slug with a snail trail following behind. Their eyes are located at the tip of the two upper most tentacles represented as tiny black specks. Their two lower tentacles, which both smell and feel, help navigate their slow journey across the forest floor. With tongues like conveyor belts, called radula, banana slugs are able to pulverize and eat anything from dead animals, to poop, to plants and mushrooms. Eating stuff on the forest floor is their specialty job.

Despite their tender look and charming color, banana slug slime packs a punch to any would-be predator. When threatened, this slug curls into a ball and secretes a white slimy mucus that makes any predator want to immediately spit it out. Surprisingly, some predators too hungry to let this stop them, such as Raccoons, have been seen on campus rolling banana slugs in dirt to buffer the slime and then gulping them down in one swallow. The Pacific Giant Salamander has also been witnessed choking down the slimy yellow mascot.

Banana Slug Ariolimax dolichophallus. Photo © Greg Bodi.

There are three main salamanders that find their homes in Cave Gulch. The earthworm sized Slender Salamander usually hangs out under rocks or fallen limbs along with their friend and fellow salamander, the Yellow Eyed Ensatina.

Slender Salamander Batrachoseps atteduatus. Photo © Lauren McEvoy.

The coloring of the Yellow Eyed Ensatina (brown back, orange stomach, and yellow patches under the eyes) mimics that of the highly toxic Rough-Skinned Newt. Because of this adaptation, their coloring deters predators from snacking on their tasty non-toxic meat.

Yellow Eyed Ensatina Ensatina eschscholtzii xanthoptica. Photo © Lauren McEvoy.

The Pacific Giant Salamander is rarely if ever seen but their larvae can be easily found in summer months swimming in perennial pools along Cave Gulch. The Giant Salamander is not only the heaviest terrestrial salamander in the world but they also have extremely sharp dagger-like teeth that give them hierarchy in the food web over other salamanders. Equipped with a deadly set of pearly whites, the Giant Salamander can eat crickets, shrews and even the tasty Yellow Eyed Ensatina.

Pacific Giant Salamander Dicamptodon ensatus Photo © Jeffrey Marsten.

Salamanders are very sensitive to any oils and salts that we naturally have on our hands so it’s best to admire without touching.

Birds in The Trees

Chestnut-backed Chickadee Poecile rufescens. Photo © Kevin Cole.

There are many birds among the forests of Cave Gulch whose calls and songs are melodious to the avid birder and the occasional passerby alike. There are roughly 40 different species of birds that visit Cave Gulch yearly, some more commonly seen than others. The tiny brown and white Chestnut-backed Chickadee is found year round in the Gulch. It often chats in groups and occasionally hangs from the tips of branches while looking for seeds or bugs to munch on.

Hairy Woodpecker Picoides villosus. Photo courtesy of Mdf.

You may also hear the echo of the Hairy Woodpecker in a faraway tree. The call resembles the sound of a dog’s squeak toy. Usually seen pecking holes in tree trunks, those who catch a glimpse of the Hairy Woodpecker will never forget its exceptionally long beak, fuzzy nose and striking red cap.

Take the Self-Guided Mobile Tour

This piece is part of the UCSC Natural History Tour. Download the free app with many tours of the Santa Cruz area and beyond.