Glossary of Geology Terms Used

Alluvium – Unconsolidated gravel, sand, and finer rock debris deposited principally by running water. Found locally on the floors of canyons and valleys.

Anticline – a fold in layered rock, convex upward, with older rocks toward the core.

Basement Complex – the surface beneath which sedimentary rocks are not found; the igneous, metamorphic, granitized, or highly deformed rock underlying sedimentary rocks.

Bedding Plane – the dividing plane that separates each layer in a sedimentary or stratified rock from layers below and above it.

Coast Ranges Orogeny – A time, mostly during the late Pliocene, of major deformation (mostly mountain building and faulting), metamorphism, and volcanic activity in the Coast Ranges in California.

Disconformity – an unconformity in which the beds above and below an erosion surface are concordant. These mark breaks in the geologic timeline.

Facies – an assemblage or association of mineral, rock, or fossil features reflecting the environment and conditions of origin of the rock.

Headward Erosion – the lengthening of a valley or gully, or of a stream, by erosion at the valley head

Orogeny – period of intense mountain building by way of folding, thrusting, or volcanism

Perennial – flowing year round, as opposed to Intermittent, flowing seasonally

Syncline – a downward fold in layered rock, primarily sedimentary rocks, caused by compression forces ; opposite of an Anticline

Terrace – Step-like landform consisting of a flat tread and a steep riser, commonly of fluvial (river), lacrustine (lake), or marine origin.

Thrust Fault or Zone – Gently inclined reverse fault along which one block is thrust over the other.

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