Petrified Links
The Trail of the Petrified Forest
The Pit Tree The Giant The
Queen Ollie Bockée Tree The
Monarch The Stevenson
Great redwood trees turned to stone attract thousands of visitors every year to this private park in the hills of eastern Sonoma County. Rich in history from the late 1800s, the Petrified Forest is a perfect example of explosive volcanic activity.
Redwood trees up to 8 feet in diameter and hundreds of feet high were blown down like match sticks in the flow of a wave of ash from a major volcano to the north and east. They were subsequently deeply buried by ash and preserved by replacement of organic material by fine-grained silicon and oxygen (chalcedony). Modern uplift and erosion has exposed the tips of the trees and final excavation by man results in the display we see today.
The park itself was established in 1910 by Ollie Bockee and her family. The Petrified Forest is a privately owned attraction, with a fine museum devoted to the origin of the fossils and geology of the area. A gift shop with crystals, petrified wood and books are available. An admission is charged for a 20 minute walk through the natural displays. Interpretive signs at major points are aimed at the lay person to help understand the processes that result in the preservation of these spectacular fossils.
A short hike will allow you to see all the major tree exposures in the park. A meadow hike, by appoinment only, leads to views of Mt St Helena and a white slope called the Ash Fall. 8 major and 4 minors (gulley, wood piles and Stevenson plaque) displays are available on the main walk. The hike starts in the patio area behind the gift shop. The first attraction is a collection of petrified logs . These have been collected from around the area. Most are gray to white, the typical color of petrified wood here and display growth rings on closer examination and ridges on the surface formed by the thick bark of the original redwood trees. The trail leads uphill to the left through a mixed woodland of oaks, firs, bay and manzanita. Low rounded outcrops of gray rock is volcanic ash or tuff, very soft here, it is not welded or hardened and probably formed as an ash fall.
The
first petrified tree exposed is called the Pit tree because it is exposed
in a 15 foot deep pit. It is the only pine preserved in the park, with
finer ridges in the bark, unlike the more typical redwood. It is 43 feet
in length and 2 feet in diameter, hardly a giant, but evidence that this
was a cool, moist environment when the trees were preserved. White-gray
ash in the walls of the pit is more tuff.
The trees must have been buried rapidly by a great deal of ash in order for them to be preserved. The tops of the trees here point to the southwest, indicating that they fell in that direction. They also slope up toward the tips, so it is unlikely that they fell down a slope. The uniform direction of tops and the preservation of the trees indicates they were blown down by a volcanic blast like Mt. St. Helens and rapidly buried deeply by an ash fall. Further past the Pit Tree and down slope is the gulley tree, a series of broken fragments of an originally larger tree, this one a redwood. The trail climbs up to the right and enters into a meadow area surrounded by Manzanitas.
An exhibit on the right describe the tuff and its origin as a cloud of gas, glass and ash, which swept down the side of a volcano flattening the trees in its path. Dark fragments of volcanic rock and glistening shards of volcanic glass are visible in the dominantly ash-rich rock. Another display on the left up the trail is a statue of Petrified Charlie and his mule, and a woodpile of petrified logs from around the property.
The Giant is the next tree, a handsome specimen of a redwood, with deeply furrowed bark. This extinct redwood is a close cousin of the present giants living in the coastal regions. Now 60 feet long and 6 feet in diameter, it must have been much larger originally, because of the 3 feet thickness at the top. You can also see the beginning of the root ball in the deeper part of the excavation. Again the light-colored rocks of the walls are tuff made from the volcanic ash that buried this area.
Several large logs are on display between the Giant and the next exhibit, the Queen tree. Here you can see the fine detail of growth rings, knotholes, where limbs once were and the sparkle of "druzy" quartz, tiny crystal faces of quartz which sparkle in the light. These form during the petrifaction process where more silica is available and the crystals have longer time to form, this allows them to grow.
The
Queen tree has an oak growing out of it, and is one of the largest in
girth, 8 feet in diameter and 65 feet long, again with a prominent root
ball. This tree was also probably taller. Its age was 2000 years when
it fell. It also fell in a southwest direction, uphill, so must have been
blown over by a volcanic explosion.
The Ollie Bockée Tree is a continuation of a project that started years ago.
With modern technology ( a backhoe) and the sweat of present workers,
a 70 foot long section has been exposed, with 2 trees, criss-crossed to
each other. The root ball has not been unearthed as yet, but work will
continue until it is exposed. These also are redwoods, with tops pointed
to the southwest, the same direction as all other trees.
At
105 feet long and 6 feet in diameter, The Monarch or "tunnel"
tree is the largest intact petrified tree in the world. Ribbed bark and
detail exposed indicate it is also a coast redwood. Large knotholes are
preserved, showing that many branches of the tree existed. These branches
were thinner and did not have the thick bark that the main trunk had,
so were probably burned during the initial volcanic blast.
The "Rock of Ages" display shows another tree, somewhat fragmented here, which protrudes from tuff.
The "Robert Louis Stevenson" tree has the best display of growth rings and surface detail. Druzy quartz also adorns the surface. This is the only tree with an odd orientation. it is more west than the others. A great cross-section of the tree 5 feet in diameter shows the growth rings visible in redwoods today.
The
Stevenson-Petrified Charlie plaque commemorated the meeting of these two
giants of history in 1880 and the discovery of the major trees by Petrified
Charlie in 1870. Two large logs flank the planks plaque is set in a monument
of smaller logs.
A small pile of petrified wood stumps, collected throughout the forest, is the last exhibit. The trail then takes you back to the patio, where the gift shop and museum await.
Written by Terry Wright, Professor of Geology at Sonoma State University
The Petrified Forest• 4100 Petrified Forest Road Calistoga, Ca 94515 • manager@petrifiedforest.org • 707.942.6667