DeLaveaga- The Epicenter of Disc Golf
3-disc trip
On a recent trip to California I ended up with an unexpected extra day on my hands. So while my friends in the area went to work, I spent a Friday visiting one of the great old Disc Golf Courses, DeLaveaga in Santa Cruz. I had no discs with me so I stopped at the local convenience store, picked up a Tern, River and Wizard, and went to throw some discs and study the geology of the epicenter of disc golf.
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Figure 1: (Wood 2016) The Epicenter of Disc Golf
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The Disc Golf Course at DeLaveaga was originally put in for the 1984 World Disc Golf Championships, cleaning up what had been a dumping ground and poison oak jungle behind the city of Santa Cruz. The course eventually became permanent and its disc golf club became stewards for both the course and the wilderness that surrounds it. Many of the original holes still exist while 11 more have been added to create the current 29 hole layout. The last hole, Top of the World has become one of the signature holes in all of disc golf a 500 foot hole with a nearly 100 foot elevation drop. The vista from the tee with Santa Cruz and the Pacific Ocean as the backdrop is spectacular and memorable way to end a round.
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| Figure 2: (Wood 2016) Hole 17 basket Purisima Formation on left. |
Disc golf in an active plate margin
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Figure 3: (Stouffer 2006, text from USGS 2006) Map of the
modern San Andreas Fault in relation to the greater
Plate-tectonic setting in western North America and the
northeastern Pacific Ocean Basin. The San Andreas Fault system
connects between spreading centers in the East Pacific Rise
(To the south) and the Juan de Fuca Ridge and Medicino fracture
zone system (to the north). The San Andreas fault system has
gradually evolved since middle Tertiary time. The right-lateral
offset that has occurred on the fault system since that time is
about 282 miles; however, the fault system consists of many
strands that have experienced different amounts of offset.
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Though both California and New England are filled with faults, folds and exotic terranes, the time when the events occurred is very different. In New England you are surrounded by layer upon layer of ancient history, the mountains and volcanoes are mere shadows of their active peak millions of years ago. Along the California coast, the geology is fresh and active, happening before our eyes. DeLaveaga is located about 8 miles west of the San Andreas Fault, which defines the boundary between the North American and Pacific tectonic plates. The San Andreas Fault is a transform fault which means that the rocks on both sides of the fault are moving parallel and in opposite direction of each other, like two hands slipping past each other. The west side of the fault is moving to the northwest at a rate of approximately 4 cm per year. Though the San Andreas is the most well-known fault in California there are thousands of other faults. Some are large, with kilometers of displacement and can cause major earthquakes, others are small with only a few feet of displacement and only minor earthquakes, some are no longer active and are only recognizable due to the rocks they displace or geomorphic features they cause. In the San Francisco Bay Area the plate boundary movement is spread across several of these faults, including the San Andrea, Hayward, Calaveras and San Gregario faults. Rather than a single line, the boundary between the North American Plate and the Pacific Plate is really zone of movement encompassing these parallel faults. Delaveaga is within this zone, sitting between the San Andreas and the San Gregario Fault and a lot of its geology is a result of the deformation due to these faults movements.
1989
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Figure 4: (H.G. Wilshire US. Geological Survey 1989)- Large
cracks in ground formed during earthquake near house
on summit road Santa Cruz Country CA.
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A consequence of being on an active plate boundary is the occurrence of earthquakes. If you rub your hands together there is friction, resistance to movement that can cause your hands to stick together. Like your hands, the rock units on both sides of a fault will often stick together as they move pass each other due to gradual movement over time. Eventually the stress caused by this movements becomes large enough that the rocks move quickly accommodating all of the movement at once; this is an earthquake. Every year many Earthquakes are felt in the Santa Cruz area on many different faults, large and small. Most of these earthquakes are small and cause little or no damage but every once in a while a large earthquake occurs. The last major earthquake in this region was in 1989. This is the quake famous for disrupting the 1989 World Series. I remember watching the TV just before the game got started, the screen going to static and then the announcers coming back on the air as the shaking wound down. Instead of a baseball game I sat that evening transfixed by the coverage of collapsed bridges and buildings. It was my first experience with a Natural Disaster, live and in real time. The earthquake was a magnitude 6.9 earthquake, its epicenter in the mountains northeast of Santa Cruz. The shaking lasted for 15 seconds and reached VIII on the Mercalli intensity scale throughout the Santa Cruz area, causing some buildings to collapses, cracking roads and causing many landslides in the mountain. In the end 63 people were killed in the bay area and about 6 billion dollars worth of damage was caused. The shaking would have been quite dramatic on the course, one would have wanted to move to one of the open spots on the course to wait it out as some limbs and maybe some old trees would have come tumbling to the ground a frightful experience but once away from trees, a disc golf course would be one of the safest places to be during an earthquake, much better that at a desk, on a bridge or at an indoor climbing wall.
Purisima Formation
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Figure 5 (Wood 2016) View from tee of hole #2, Looking
up-slope of hill at horizontal layers of Purisima Formation,
more resistant layers form steeper slopes and softer layers
gentler slopes.
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The same forces that are responsible for the Earthquakes are also in some ways responsible for the bedrock the course sits on. DeLaveaga Disc Golf course is underlain by sandstone and siltstone of the Purisima formation. The Purisima was formed between 6-2 million years ago from sediment eroded from the Santa Cruz Mountains as they were uplifted due to deformation caused movement along the plate boundary. The Purisima formation was deposited in relatively shallow water (usually less than 200m) near the source of the sandy sediment, probably in and environment not to unlike the modern Central California Coast. The sediment was hardened into rock then both uplifted above sea level and broken up by local faults into several large blocks that stretch from Santa Cruz to Point Reyes. Abundant fossils are found in the Purisima formation and ppint to its shallow Marine Origin, including various mollusks shells and whale bones. Though the best preserved fossils are found on the coast near Santa Cruz and near Ano Nuevo State Park, casts and molds of mollusks can be seen in outcrops on holes #2, #3 and #27 as well as occasionally elsewhere on the course. Casts and molds are created when sediment fills in the cavity or surrounds an organism. After the original shell material dissolves away an imprint or shape of the shell is left. The best place to look for these casts and fossils is on hole #2, where you climb through several different layers that are full of molds or casts, often reddish in color. Though detail of the shells has been lost, the general shape and quantity of these creatures can still be seen. The layers of the Purisima are nearly horizontal, dipping slightly southward towards the coast due to ongoing uplift of the Santa Cruz Mountains. You can clearly see the horizontal nature of the formation on hole 2, 7 and 17 where slightly more erosion resistant layers make small 1-3 foot high ledges and on hole 19 where the basket is often on the top of an exposed resistant layer.
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Figure 6 (Wood 2016) Hole #2 fairway. Molds and Casts of mollusks in Purisima Formation.
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Figure 7: (Wood 2016) Hole #2 Purisima Formation, mold or cast of mollusk
with reddish coloration likely due to iron mineralization.
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Figure 8: (Wood 2016) Hole #2 fairway looking towards basket. More resistant layer
of Purisima forming slight step in the hillslope.
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Figure 9 (Wood 2016). Hole #8 Basket, Purisima formation and large tree.
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Fractures
With its location near many faults it is not surprising that the bedrock at DeLaveaga is heavily fractured. Because of the similar appearance of much of the Purisima, it is difficult to tell if there has been much movement on most of these fractures. When looking up the hill on 2 and 27 the layers appear to be continuous and show no vertical movement. In some places fractures separate rocks of slightly different coloration, these could represent small fault offsets but also could just be coloration variations due to water percolation or other non-deformational causes. Also some fractures have been mineralized, mostly with calcium carbonate. The different directions, offset and mineralization on the fractures record a complex history of deformation due to stress put on the area from being in the middle of a plate boundary.
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Figure 10 (Wood 2016) Hole #15. Purisima formation showing multiple parallel
joints with no mineral fill. These joints are likely related to the tectonic
stresses due to the plate boundary.
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Figure 11: (Wood 2016) the Basket for #20 sits on the top of a more resistant
Purisima Forrmation layer. Numerous joints can be seen on the bedrock surface.
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Figure 12: (Wood 2016) Hole #21 basket. Fracture in Purisima formation
separating two layers of Purisima with differing colorations. Possibly
a small fault.
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Marine Terraces
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Figure 13: (Wood 2016) View from #27 tee “Top of the World”. Note
fairway below and hills in midground are part of the
upper terrace. Background is the lower terrace around Santa Cruz.
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If you drive down the Pacific Coast between Santa Cruz and Half Moon Bay, you will notice that the land rises from the ocean in a step like pattern with flat plateau separated by steep slopes. The flat plateaus are wave cut terraces, formed by wave action eroded the bedrock when the sea level was at that elevation in the past. The terraces along this part of the California Coast are not caused by sea level rising and falling, but by the land rising while sea level has remained “relatively” constant. The Santa Cruz area has been uplifted in recent time because the San Andreas fault system, though mostly transform in nature, has a compressional component due to its bending to the left (much like the San Bernardino Mountains near Los Angeles) causing the area to gradually rise in elevation. This uplift has lifted old terraces to their current positions tens to hundreds of feet above sea level. As you drive up to DeLaveaga Park you start on a lower terrace level in the residential neighborhoods, go up a steep wooded slope and reach a higher terrace around the ball golf course area (This is my amateur interpretation, I found no literature on the terraces exactly in this exact area, all the literature focused on terraces a few miles to the north or south). This upper terrace extends back to the disc golf course area and is the flat surface that many of the holes of the course play on. The Top of the World hill represents the back end of the terrace, rising above the flat platform like a cliff backing a beach. Being older than the lower terrace the upper terrace is much more heavily eroded. Gullies have cut deeply into the margins of the terrace and are in the process of cutting it down to the lower level. It is this active erosion that is the cause of the extreme topography at the margins of the course, including steep drop offs to the right of holes 3-9 and to the left of holes 20-21. Without this terrace, the course would look like any other mountain slope in the area, the terrace gives it the flat areas that make both disc and ball golf work well in the park.
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| Figure 14: (Wood 2016) Davenport CA, Wave cut terrace above current coastline. This terrace is likely equivalant to the lower terrace below DeLavega Park. |
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Figure 15: (Tommy Slaton 2010) Hole #27 from basket looking to tee.
Lower part of fairway is part of wave cut terrace, break of hill most likely
represents the inland extent of the terrace.
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Hope you enjoyed this trip out to California as much as I did. Up next is a trip to New Hampshire to see Yoda’s Swamp, rock cairns and road cuts at Otter Brook.
Course Webpage
contains info on history of course and hole by hole tour.
References
Brabb, E.E. (1997) Geologic Map of Santa Cruz County California [geologic map]. https://pubs.usgs.gov/of/1997/of97-489/scruzmap.pdf
Powell, Charles L. United States Geological Survey Open File Report 98-594. (1998) The Purisima Formationand Related Rocks (Upper Miocene – Pliocene), Greater San Francisco Bay Area, Central California. https://pubs.usgs.gov/of/1998/of98-594/of98-594_2a.pdf
Powell, Charles L, Barron, John A., Sarna-Wojcicki, Andrei M., Clark, Joseph C., Perry, Frank A.,
Brabb, Earl B., and Fleck, Robert J., USGS Professional paper 1740. (2007) Age, Stratigraphy and Correlations of the Late Neogene Purisima Formation, Central California Coast Ranges. http://pubs.usgs.gov/pp/2007/1740/pp1740.pdf
United States Geological Survey. (1993). Historic Earthquakes, Santa Cruz Mountains (Loma Prieta), California 1989. http://earthquake.usgs.gov/earthquakes/states/events/1989_10_18.php
United States Geological Survey. (2006) Geological History of the San Andreas Fault System. http://geomaps.wr.usgs.gov/archive/socal/geology/geologic_history/san_andreas_history.html
Weber, Gereld E and Allwardt, Alen (2001). The Geology From Santa Cruz to Point Ano Nuevo- The San Gergario Fault Zone and Pleistocene Marine Terraces. https://pubs.usgs.gov/bul/b2188/b2188ch1.pdf
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