ABSTRACT
Five differential equations that interrelate uplift, erosion, and deposition along stream systems that cross the mountain fronts of the northern Mojave Desert were used to appraise three classes of Quaternary tectonism. Class 1 (active tectonism) terrains are characterized by mountain-front sinuosities of 1.2 – 1.6, unentrenched alluvial fans, elongate drainage basins with narrow valley floors and steep hillslopes even in soft materials. Class 2 (moderate to slightly active tectonism) terrains are generally characterized by mountain-front sinuosities of 1.8 – 3.4, entrenched alluvial fans, large drainage basins that are more circular than class 1 basins in similar rock types, steep hillslopes and valley floors that are wider than their floodplains. Class 3 (tectonically inactive) terrains are characterized by mountain-front sinuosities of 2 to 7, pedimented mountain fronts and embayments, steep hillslopes only on resistant rock types, and few large integrated stream systems in the mountains.
Marked contrasts of landscapes, that are due to different relative rates of base level fall, are present north and south of the strike-slip Garlock fault. In a northern sub-area, class 1 terrains generally occur on the west sides and class 2 terrains on the east sides of the eastward tilted116 fault – block mountains. Extreme tectonic stability is shown by the dominance of class 3 terrains south of the fault. Pedimentation has left only remnants of the formerly more extensive mountain ranges and their drainage basins. Between the extremes of these two subareas is a transitional sub-area north of the Garlock fault, where the magnitudes of Quaternary uplift of the mountain fronts decrease towards the south.
