A chunk of Marin Headlands Terrane shadowed by the Golden Gate Bridge, R. Forest
Terrane (not terrain):
A structural entity which has a stratigraphic sequence and history quite distinct from those of adjacent units
A substantial block of rock – a crustal block – that is bounded by faults and usually contrasts with surrounding rock bodies. Terranes can be far-travelled blocks accreted to a continent – commonly called exotic terranes; or terranes can be displaced to another portion of the same continent
A large block of crust with a distinct geologic character, originally part of the same crustal plate
Large or small packets of rock involved in dynamic plate movements, and bounded by faults. Each packet, or terrane, can totally differ in composition, or differ only slightly, from neighboring packets/terranes
(Definition references are listed at the bottom of the Geomorphology Word of the Day home page)
Where in California:
With California’s overwhelmingly dynamic tectonic and geologic history, a multitude of terranes exist across the State. Focusing-in on the Coast Ranges geomorphic province and its geomorphic origins as an accretionary wedge, there is no shortage of distinct and varied terranes in this highly faulted and fractured landscape dominated by the goulash of the Franciscan Formation.
In the San Francisco Bay Area alone there are at least 16 major geologic terranes found within the Franciscan Complex, the Great Valley Complex and the Salinian Complex. These include: the Alcatraz Terrane; the Burnt Hills; the Cazadero; the Devil’s Den Canyon; the Lake Sonoma; the Marin Headlands; the Nicasio Reservoir; the Novato Quarry; the Permanente; the San Bruno Mountain; the Yolla Bolly; the Del Puerto; the Elder Creek; the Healdsbug; the Point Arena; and the Salinia Terranes.
