Active Faulting along the Black Mountains Front,
Death Valley, California
The Black Mountains are currently rising with respect to the floor of Death Valley. This activity occurs along the north-trending Black Mountains fault zone. The fault zone displays abundant evidence for recent movement, which, in turn, shapes the mountain front. This recent activity also greatly influences the overall present landscape of central Death Valley.
The visitor to Death Valley can see the effects of this active uplift by viewing the Black Mountains from both the valley floor along the Badwater Road, and from the range crest, at Dantes View. From the valley floor, one can see an extremely abrupt transition from valley floor to mountain, fault scarps, wineglass canyons, and faceted spurs. Bedrock at the mountain front also gives some information about the faulting. From Dante's View on the range crest, one can see the overall character of the Black Mountains as well as the surrounding ranges.
Click on the headings below for photos and more text.
Transition from valley floor to mountains.
The Black Mountains front is controlled by the Black Mountains fault zone. As this fault is recently active, the transition from valley floor to mountainous topography is incredibly abrupt--because erosion has not had the time to cut back into the mountain front.
Fault scarps in alluvial fans provide clear-cut evidence for recently active faulting along the Black Mountains front. In these places, faulting must be recent because it cuts recently deposited alluvial fan material.
When viewed from the correct angle, most canyons in the Black Mountains resemble wineglasses: the alluvial fan forms the glass's base while the narrow canyon behind it broadens with increasing elevation to form the stem and bowl. Wineglass canyons indicate recent uplift. Their steep "stems" form by erosion of the canyon floor immediately behind the fault soon after an uplift event. With time, stream erosion and mass wasting processes widen the canyons to form bowls. Later uplift events re-form the stems while erosion continuously widens the canyon upstream. In the Black Mountains, many of the canyons begin with dryfalls at their mouths and therefore have near-vertical stems.
Faceted Spurs. Many west-trending ridges, or spurs, in the Black Mountains end abruptly at an elevation of about 1500'. Below the spur lies the relatively smooth, steep face of the mountain front, which if bounded by canyons, will be triangular in shape. The spur therefore appears "faceted", that is, abruptly truncated by the fault zone at the front of the range. Faceted spurs indicate recent uplift because the triangular-shaped regions between the canyons experienced very little erosion since faulting began.
Smaller faults. Much of the bedrock along the Black Mountains front is broken or crushed from movement along the Black Mountains fault zone. It also contains small-scale faults which probably formed during movement on the main zone. These faults locally display smooth, striated surfaces that form by abrasion during slip; the striations form parallel to the direction of movement. Many of the smaller faults along the front of the Black Mountains have striations which trend obliquely to the mountain range. Therefore, the fault motion which uplifted the Black Mountains had a strong sideways, in addition to its up-down, component.
The Black Mountains from Dantes View. elevation
From Dantes View, one can look both east and west to see part of the Basin and Range Province: a landscape that consists of alternating mountain ranges and intervening basins. Like Death Valley, this topography formed by crustal extension, where mountains rose relative to basins along large normal faults.
The view from Dantes View also shows the asymmetry of the Black Mountains. They have a gentle east flank and an incredibly steep west flank. This asymmetry reflects eastward tilting of the range as it rises along the Black Mountains fault zone. It develops a steep western side immediately behind the fault, and a gentle eastern side, approximately parallel to east-tilted rocks of the range. Click here, or on the photo above to see both sides.
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