The Transverse Range - Info from Wikipedia

The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie between Santa Barbara and San Diego counties. They derive the name Transverse Ranges due to their east–west orientation, making them transverse to the general north–south orientation of most of California's coastal mountains.

Most of the system lies in the California chaparral and woodlands ecoregion. Lower elevations are dominated by chaparral and scrubland, while higher elevations support large conifer forests. Most of the ranges in the system are fault blocks, and were uplifted by tectonic movements during the Cenozoic Era. West of Tejon Pass, the primary rock types are varied, with a mix of sedimentary, volcanic, and metamorphic rocks, while regions east of the pass are dominated by plutonic granitic and metasedimentary rocks.

Geography

Most of the Transverse Ranges are bounded to the north and east by the San Andreas Fault, which separates the ranges from the California Coast Ranges and the Peninsular Ranges. Notable passes along the fault include Tejon Pass, Cajon Pass, and San Gorgonio Pass. Components of Transverse Ranges to the north of the fault include the Tehachapi Mountains and the San Bernardino Mountains. The western and southern boundaries are generally acknowledged to be the Pacific Ocean and various alluvial valleys and basins. Major passes not along the San Andreas Fault include Gaviota Pass, San Marcos Pass, the Conejo Grade, Newhall Pass, and Cahuenga Pass.

The mountains are notable for being steep and difficult to traverse across. On its northern end, there are few passes that are sufficiently low or wide enough to accommodate significant volumes of traffic. This has resulted in situations where major cities are linked to the rest of the state by relatively few number of roads; for example, the vast majority of traffic between the Central Valley and the Los Angeles area is routed through Tejon Pass. This results in significant traffic issues throughout Southern California when a pass has to be shut down due to heavy snow or construction. Occasionally, such as Santa Barbara during the 2005 La Conchita landslide, major cities may be cut off from timely road access to the rest of Southern California.

The Transverse Ranges manifest themselves as a series of roughly parallel ridges with an average height of 3,000–8,000 feet (910–2,440 m). The ranges are dissected by young, steep streams of relatively low flow rate; as a result, there is high topographic relief throughout the range, and other than in marginal areas (e.g. the San Fernando Valley) and a few river valleys (such as Lockwood Valley and Big Bear Valley), there are no large, flat basins within the ranges.

Major peaks of the Transverse Ranges with at least 500 feet (150 m) of prominence, listed by height:
1 Mount San Gorgonio, 11,503 feet (3,506 m), San Bernardino Mountains.
2 Anderson Peak, 10,840 feet (3,300 m), San Bernardino Mountains.
3 Mount San Antonio (Old Baldy), 10,068 feet (3,069 m), San Gabriel Mountains.
4 Sugarloaf Mountain, 9,952 feet (3,033 m), San Bernardino Mountains.
5 Mount Baden-Powell, 9,407 feet (2,867 m), San Gabriel Mountains.
6 Galena Peak, 9,324 feet (2,842 m), San Bernardino Mountains.
7 Throop Peak, 9,142 feet (2,786 m), San Gabriel Mountains.
8 Telegraph Peak, 8,985 feet (2,739 m), San Gabriel Mountains.
9 Cucamonga Peak, 8,862 feet (2,701 m), San Gabriel Mountains.
10 Mount Pinos, 8,847 feet (2,697 m).
11 Ontario Peak, 8,693 feet (2,650 m), San Gabriel Mountains.
12 Delamar Mountain, 8,402 feet (2,561 m), San Bernardino Mountains.
13 Cerro Noroeste, 8,280 feet (2,520 m).
14 Mount Islip, 8,254 feet (2,516 m), San Gabriel Mountains.
15 Gold Mountain, 8,239 feet (2,511 m), San Bernardino Mountains.
16 Bertha Peak, 8,205 feet (2,501 m), San Bernardino Mountains.
17 Frazier Mountain, 8,017 feet (2,444 m).
18 Iron Mountain #1, 8,010 feet (2,440 m), San Gabriel Mountains.
19 Reyes Peak, 7,510 feet (2,290 m), Pine Mountain Ridge.
20 Haddock Mountain, 7,431 feet (2,265 m), Pine Mountain Ridge.

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Geology

The Transverse Ranges have a complex geological history, and the rock composition of the ranges are varied.

Tectonics

The Transverse Ranges represent a complex of tectonic forces and faulting stemming from the interaction of the Pacific Plate and the North American Plate along the San Andreas Fault system. Their orientation along an east–west axis as opposed to the general southeast-northwest trend of most California ranges results from a pronounced step in the San Andreas Fault, the cause of which is a subject of intensive ongoing study. The San Andreas Fault is a dextral strike-slip fault with a right step, causing the mountains. Their elevation is somewhat better understood as a consequence of this step. The crust atop the Pacific Plate south of the ranges does not easily make the turn westward as the entire plate moves northwestward, forcing pieces of the crust to compress and lift.

The crust which comprises the Transverse Ranges is part of what is known as the Salinian Block, originally a piece of the North American Plate which was broken off what is now northwestern Mexico as the Gulf of California rifted open.

Physiographically, the Transverse Ranges are a distinct physiographic section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System. They exhibit extreme differences in geologic age and composition, varying from sedimentary rocks in the western Santa Ynez and Santa Monica mountains to primarily granitic and metamorphic rock in the eastern regions, where they terminate abruptly in the San Gabriel and San Bernardino mountains.

Between this set of ranges and the Peninsular Ranges is the complex Malibu Coast—Santa Monica—Hollywood fault, which exists as the border between these two mostly geologically unitary provinces.

Rocks

The rock types in the ranges are extremely varied. The oldest rocks are of Proterozoic age, and are found in the San Gabriel Mountains, the San Emigdio Mountains, and the San Bernardino Mountains. The Jurassic-Cretaceous Franciscan Assemblage is found in the western section of the ranges. Exposed plutonic rocks from the Mesozoic, mostly granites, can be found on Mount Pinos and generally in regions east of Tejon Pass. Finally, the youngest rocks are Cenozoic sedimentary and volcanic rocks that can be found throughout the ranges.

Some limestones can be found in the Santa Ynez Mountains; these are remnants of ancient marine fossils. Some rhyolite dikes, presumably formed from rifting processes, can be found around the San Andreas Rift Zone.