This subsection comprises the higher mountains of the Peninsular Ranges from Agua Tibia Mountain southeastward to the Mexican border.   The climate is temperate and subhumid; it is affected by elevation more than by marine influence.  MLRA 22c.

Lithology and Stratigraphy.  This subsection contains mostly Mesozoic granitic rocks.  Also, there are some Pre-Cenozoic granitic and metamorphic rocks and some Mesozoic mafic plutonic rocks.  There are small areas of Pleistocene sediment and Recent alluvium.

Geomorphology.  This is a subsection of moderately steep to steep mountains with rounded summits, broad valleys, and rolling plateaus.  There is a drainage divide in the subsection,  between streams running southwest to the coast and streams running east to the Salton Trough.  The subsection elevation range is from about 2000 feet up to 6140 feet on Palomar Mountain and 6515 feet on Cuyamaca Peak.  Mass wasting and fluvial erosion and deposition are the main geomorphic processes.

Soils.  The soils are mostly shallow Entic Haploxerolls, Entic and Ultic Haploxerolls, and Mollic and Ultic Haploxeralfs.  Also, there are Rhodoxeralfs on mafic plutonic (diorite and gabbro) rocks.  The soils on alluvium in valleys are mostly Haploxerolls.  The soils are leached free of carbonates.  They are well drained.  Soil temperature regimes are mostly mesic, and soil moisture regimes are xeric.

Vegetation.  The predominant natural plant communities at lower elevations are Chamise series, which is typically on shallow or stony soils, Mixed chaparral shrublands, and Live oak chaparral shrublands.  Coast live oak series and Needlegrass grasslands are common in valleys.  There are small areas of Engelmann oak series.  The predominant natural plant communities at higher elevations are Coulter pine series, Jeffrey pine series, Big-cone Douglas-fir series, Mixed conifer series, and Black oak series.  Also, there are Montane meadow habitats.  Cuyamaca cypress stands and Tecate cypress stands are unique in this subsection.

Characteristic series by lifeform include:

Grasslands: Foothill needlgrass series, Nodding needlegrass series, Purple needlegrass series, Quillwort series.

Shrublands: California sagebrush - California buckwheat series, California buckwheat - white sage series, Chamise series, Chamise - bigberry manzanita series, Chamise - white sage series, Chamise - cupleaf ceanothus series, Chamise - Eastwood manzanita series, Chamise - mission-manzanita - woollyleaf ceanothus series, Chaparral whitethorn series, Greenleaf manzanita series, Mixed scrub oak series, Mountain whitethorn series, Scrub oak series, Scrub oak - birchleaf mountain-mahogany series, Scrub oak - chamise series, Scrub oak - chaparral whitethorn series, White sage series.

Forests and woodlands: Bigcone Douglas-fir series, Bigcone Douglas-fir - canyon live oak series, Birchleaf mountain-mahogany series, Black oak series, Canyon live oak series, Coulter pine series, Coulter pine - canyon live oak series, Coast live oak series, Cuyamaca cypresses stands, Engelmann oak series,  Incense-cedar series, Interior live oak series, Jeffrey pine series, Mixed conifer series, Ponderosa pine series, Parry pine series, White fir series.

Surface Water.  Runoff is rapid.  All but the larger streams are dry through the summer.  There are sag ponds along the Elsinore Fault Zone, but Lake Henshaw is the only natural lake, and its level has been raised artificially.  There are some reservoirs in the subsection.