| Subsection map Ecological Section map Previous Subsection Next Subsection |
This
subsection comprises the mountains and hills at intermediate elevations
on the southwest, or coastal, side of the Peninsular Ranges. It extends
from the Santa Ana Mountains southeastward to the Mexican border.
The northern part of the subsection is bounded on the northwest by the
Elsinore Fault Zone. The southwestern edge of the subsection is near
a line through the San Marcos Mountains, Woodson Mountain, Iron Mountain,
Sequan Peak, and Otay Mountain. The climate is hot and subhumid;
it is modified moderately by oceanic influence. MLRA 20d.
Lithology and Stratigraphy. This subsection contains mostly Mesozoic granitic rocks. There are some Pre-Cenozoic granitic and metamorphic rocks and some Mesozoic mafic plutonic rocks, also. There are small areas of Pleistocene sediment and Recent alluvium.
Geomorphology. This is a subsection of moderately steep to steep mountains and hills with narrow to rounded summits and narrow to broad canyons. There are some rolling plateau surfaces, too. The streams run southwestward toward the ocean, but San Luis Rey River initially runs parallel to the trend of the Peninsular Ranges and takes a 90° turn before running to the ocean. Many of the streams have alluvial plains a few hundred yards wide, or even wider in places. The subsection elevation range is about 1200 feet to 4000 feet. Mass wasting and fluvial erosion are the main geomorphic processes.
Soils. The soils are mostly shallow Typic Xerorthents, Typic Xerochrepts, and Typic Haploxeralfs on granitic rocks. Also, there are Rhodoxeralfs on mafic plutonic (diorite and gabbro) rocks and Lithic Xerorthents, Haploxerolls, and Haploxeralfs on other kinds of rocks. The soils of floodplains and terraces are mostly Typic Xeropsamments, Cumulic Haploxerolls, and Typic Haploxeralfs. Most of the soils are leached free of carbonates. The soils are well drained. The soil temperature regimes are mostly thermic. Soil moisture regimes are xeric.
Vegetation. The predominant natural plant communities are Coast live oak series, Chamise series, which is generally on shallow or very stony soils on south-facing slopes, Mixed chaparral shrublands, and Coastal sagebrush series.
Surface Water. Runoff is rapid. All but the larger streams are dry through the summer. Natural lakes are absent.
| Subsection map Ecological Section map Previous Subsection Next Subsection |