A Few of my Favorite Things: Birding, Botanizing and Geologizing in Del Puerto Canyon

Last weekend, geology professor and fellow natural history blogger Garry Hayes (of Geotripper and Geotripper's California Birds) graciously invited me to tag along as he led Modesto Junior College's geology club through Del Puerto Canyon and millions of years of geologic history.  I happily accepted, eager to ride along to a place known for its excellent geology, birding and wildflower displays, hoping to gain a few more nuggets of knowledge to help round out my somewhat rudimentary understanding of California's geology, which I've been working on acquiring piecemeal over the last several years.

Professor of geology, Garry Hayes, in one of a geologist's favorite places: a road cut.  Here in Del Puerto, he is pointing to the fault line between the Great Valley Sequence to the right (east) and the Coast Range Ophiolite to the left (west).

I am far, far from having a comprehensive understanding of California's geology, but I continue to read books, study the rocks, and learn from knowledgeable folks like Garry Hayes.

In the most basic terms, rocks that form the Coast Range of today are part of three major groups: the Great Valley Sequence, the Coast Range Ophiolite, and the Franciscan Complex.  The Franciscan Complex is a rather mixed up collection of rocks, including sandstone, chert and serpentinite, that were deposited in sea water before being subducted (pulled underneath) along a former plate boundary and more or less piled into the Franciscan Trench at what was once the western edge of the continent.  During the Mesozoic (around 250 to 65 million years ago; no, I couldn't remember that off the top of my head, I had to look it up) as the ocean floor was being subducted, parts of the slab of descending crust were sheared off, avoided being "stuffed into the trench" (as the Roadside Geology book I read phrases it) and formed the Coast Range Ophiolite, an ancient piece of oceanic crust.  The Great Valley Sequence, similar in age, is a layer of oceanic sediments that were deposited on top of the ocean floor, as the ancestral Sierra Nevada mountains eroded into a shallow sea.  The boundary between the Great Valley Sequence and the Coast Range Ophiolite is a fault, shown in the photo above.

A chunk of gabbro, a plutonic igneous rock that is essentially unaltered mantle, exposed in Del Puerto Canyon near a very striking quartz vein.

To more adequately and eloquently explain the geological significance of this canyon, which provides essentially the only access to this nice slice of the Coast Range (specifically, the Diablo Range within the Coast Range), I will defer to my geology professor, who has written a number of articles at Geotripper specifically about Del Puerto Canyon.  I particularly like this one, this one and this one, and at the beginning of this article is an illustration that helps to make sense of the paragraph above.  For a better understanding of the geology of California's Coast Range in general (as well as other regions), I have found the book Roadside Geology of Northern California and Central California, by David Alt and Donald W. Hyndman, to be helpful.  But really, nothing is better than having it pointed out and explained in person by an expert who is able to translate the story of the rocks and make geology really come to life.

Folds of the Franciscan Complex have a complex geologic story to tell!!

While the folded rocks of the Franciscan Complex shown above have quite the story to tell, my attention was soon captured by these neat little Duddleyas growing out of the face of the road cut.  What can I say?  I am a botanist at heart.

Dudleya cymosa, or Canyon Liveforever, possibly the subspecies paniculata

Like a good naturalist, my pages of geology notes are punctuated with off-topic scribbles that say things like "Which Blazing Star?" and "Descending call of Canyon Wren" along with an abbreviated bird list in the margin above a list of rocks and the note, "Serpentinite: metamorphic peridotite (altered mantle)."  Going through these notes later is always a treat, as I attempt to piece together a complete picture of the trip as a whole and match up which notes go with which photos of rocks.

Pictured below is the Blazing Star in question, which I believe to be Mentzelia lindleyi, Lindley's Blazing Star.  Perennials native to arid habitats, you might be familiar with our endemic San Joaquin Blazing Star or Sand Blazing Star of California's deserts.  

Lindley's Blazing Star (Mentzelia lindleyi)

The wet winter we had this year produced ideal conditions for a broad spectrum of annual wildflowers, like lupine and clarkia, which thrive in the tough conditions of road cuts and shoulders.

Chick Lupine (Lupinus microcarpus)

Clarkia, sometimes called Farewell-to-Spring, are among the last of the spring wildflowers to bloom, heralding in the hotter, drier, longer days of summer... a sign that botanists in our area should start heading up slope to take in the wildflower display beginning in the Sierra!

Elegant Clarkia (Clarkia unguiculata)

Blooming perennials along the road included dazzling purple spikes of endemic foothill penstemon, the formidable-looking Western thistle (also endemic) and hardy sticky monkeyflower, which clings to life in arid rocky outcrops.  Penstemons, by the way, are absolutely fantastic planted in a drought tolerant cottage garden!

Foothill Penstemon (Penstemon heterophyllus)

Fun botanical fact for you: thistles (including the edible artichoke) are in the aster family, along with garden favorites like daisies, sunflowers... and lettuce.

Western Thistle (Cirsium occidentale)

Widely distributed up and down California's coast and interior foothills, the range of sticky monkeyflower (such a great common name) stretches only slightly beyond the borders of our state.  Monkey flowers of the genera Diplacus, Erythranthe and Mimulus (when I was in college, they were all Mimulus!) are found across the state in a wide variety of habitats, from wetland and riparian areas to deserts.

Sticky Monkeyflower (Diplacus aurantiacus)

From spring through fall, billows of flowering California buckwheat adorn the canyons and hillsides of the Coast Range.  It is particularly abundant in the coastal sage scrub plant community of Southern California, and makes a nice addition to a native plant garden (along with many of its other buckwheat brethren.)

California Buckwheat (Eriogonum fasciculatum)

One of my favorite of California's many beautiful endemic wildflowers is the butterfly mariposa lily. (Yes, I realize that name is redundant.)  A member of the lily family, mariposa lilies grow on the thin, sandy, often granitic soils of the foothills surrounding the Central Valley and bloom in May and June.

Mariposa Lily (Calochortus venustus)

So you see, while others were busily gathering rocks, I had my eyes on other things.  Yet even so, I managed to arrive home, pockets bulging with cool rocks!

Birds are attracted to the canyon largely due to the presence of water year-round in the form of a spring (Adobe Springs) and creek (which I think is simply called Del Puerto Canyon Creek), and groups of birders regularly traverse the canyon in search of interesting species.

Creek near Adobe Spring

(Aside for birders: one of your best bets for spotting a Steller's Jay in Stanislaus county is high up in Del Puerto Canyon, right along the Santa Clara county line.  The canyon is also an excellent place for seeing Greater Roadrunners, Costa's Hummingbirds and Lark Sparrows.)

At one rock stop, I hopped out of the van and immediately heard a Bullock's oriole, singing from a Gray Pine nearby, along with a male house finch.  It took a few minutes, but we turned our attention from the rocks long enough to spot it.

Bullock's Oriole

At another spot, I heard the descending call of a canyon wren echoing off the rocky walls and, walking a few minutes up the road toward Adobe Springs, a singing black-headed grosbeak concealed in dense foliage.  We finally spotted a black-headed grosbeak at Frank Raines Park, and rounded out our trio of brilliant tropical migrants with a Western tanager father down the canyon.

Western Tanager

All in all, it was a successful and highly enjoyable day of birding, botanizing and geologizing.  I highly recommend taking a trip up Del Puerto Canyon for yourself to see what wonders await your discovery.  Spring and fall are the best times to visit, when the weather is mild.  Spring offers wildflower displays and good birding, while fall affords a glimmer of golden fall color in the cottonwoods that line the creek.  The rocks, of course, are available year-round to tell their incredible story!