Please refer to Sibley Volcanic Regional
Preserve map and "Self-guided tour of Round Top Volcano" for detailed
descriptions of stops and geologic highlights. This excellent guide was
prepared by Stephen W. Edwards, Director, Regional Parks Botanic Garden.
http://www.ebparks.org/resources/pdf/trails/sibley_text.pdf
http://www.ebparks.org/resources/pdf/trails/sibley_text.pdf
| Subject |
Photograph
number |
| Potential Cover Photographs |
3312, 3315 (both also applicable
for lava flows with tilted layers) |
| Vistas
and quarry pits |
3010, 3314, 3344 |
| Baked zone |
3316 |
| Lava flows with tilted layers |
3197, 3312, 3313, 3315 3341 (Highway 24 roadcut east of Caldecott Tunnel) |
| Columnar
jointing |
3279, 3343 |
| Basaltic
lava flow |
3347 |
| Technical
rock shots |
3345, 3346 |
| Paleosol |
3340 (Highway 24 roadcut east of Caldecott Tunnel) |
Potential Cover Photographs
3312 Steeply tilted volcanic
breccia (left) and massive basalt dome (right). Stop 4
 |
3315 Steeply tilted volcanic
breccia (left) and massive basalt dome (right). Stop 4
 |
Vistas and quarry pits
Baked zone
Lava flows with tilted layers
Columnar jointing
Basaltic lava flow
Technical rock shots
Paleosol
3010 Round Top Trail -
view northeast after Stop 1
 |
3314 Overview of park,
land bank area (closed to public), and
view North towards Tilden Regional Park after Stop 1
 |
3344 Large quarry pit at Stop 4,
with massive (vertically tilted) basalt lava dome center and right
 |
Baked zone
3316 Red-baked sequence of
air-fall tuff (ash) at Stop 8
 |
Lava flows with tilted layers
3197 Steeply tilted volcanic
breccia (left and center) and massive basalt dome (right). Stop 4
 |
3313 Steeply tilted volcanic
breccia (left) and massive basalt dome (right). Stop 4
 |
3341 Tilted layers of Miocene
Orinda Formation (alluvial-fan deposits - left gray) and Moraga
Formation (basalt lava flows - right brown).
Roadcut along Highway 24 east of Caldecott Tunnel. Note poor natural exposures on upper slopes. These are the same rocks and along the same trrend as those exposed in Sibley Volcanic Regional Preserve.  |
Columnar jointing
3279 Columnar jointing developed
during cooling of basaltic lava flow. Stop 7
 |
3343 Columnar jointing developed
during cooling of basaltic lava flow. Stop 7
 |
Basaltic lava flow
3347 Basaltic lava flow. Note
massive upper flow (left) and "jumbled" lower part (right) Stop 9
 |
Technical rock shots
3345 Gravels (will provide more
detailed caption, if necessary) OK to crop pen.
 |
3346 Tuff (volcanic ash)
breccias originated when fluid mixtures of ash, lava, and Orinda
gravels, perhaps saturated by rain, slurried and flowed down the
slopes of the volcano. OK to crop knife, if necessary. Stop 1.
 |
Paleosol
3340 Miocene Paleosols (fossil
soils) formed on abandoned portions of an alluvial-fan, whose sediments
were derived from coastal highlands where San Francisco Bay is today.
The Walnut Creek - Mt. Diablo area was the coastal plain and shallow
marine setting at that time. Roadcut along Highway 24 east of Caldecott
Tunnel.
 |