The Sky Islands of San Diego County

An ode to the Cuyamaca, Laguna and Palomar Mountains


In late October of 2003 a hunter’s errant signal fire grew out of control and proceeded to be one of the largest and most destructive wildfires to then burn in California. Overnight, westerly dry Santa Ana winds amplified the fire’s spread causing it to burn around 3,000 acres per hour. As the westerly winds pushed the fire into San Diego County’s urban wildland interface, it consumed structures and rural communities at an alarming pace. Throughout the dark of night, the fire raced through the gorges and canyons that spread out from the foothills of the Cuyamaca Mountains, making it exceedingly impossible to provide advanced warning to any communities down wind. By mid-morning the next day, 12 people were killed and thousands of acres of property had burned. The fire jumped interstates and overran fire crews with ease. And that was only the beginning. For weeks on end, the land burned. 

The Cedar Fire was not alone in the devastation it rained upon southern California. At the time of the Cedar Fire, a dozen or so fires burned throughout southern California. Other sizeable fires were burning in the mountains and foothills surrounding Los Angeles, Orange County, and other parts of San Diego County. In October of 2003, a firestorm had descended upon southern California. Years of drought and a subsequent summer of hot and dry conditions had desiccated the native vegetation. Santa Ana winds ripened the conditions and made containment virtually impossible.

The scars of those events still remain evident today. But what is equally evident is the process of renewal that followed. The ecology of southern California's chaparral and mixed evergreen habitats are no stranger to fire. Fire is a part of its ecology and thus, through eons of evolution, that ecology has adapted itself to periodic fires. And so, when the landscape burns like it has before and very likely will again, the seemingly destructive force of fire is followed by a beautiful process of renewal.

Cuyamaca Mountains, Winter of 2014 - View looking north towards Stonewall Peak and Middle Peak in the far distance. Cuyamaca Peak is out of view to the left.

Cuyamca Peak and Middle Peak suffered a great loss to its mixed evergreen & coniferous forests as a result of the fire in 2003. Much of its south facing slopes were burned bare.  

Cuyamaca Mountains, Summer of 2014 - View from the base of Cuyamaca Peak looking east towards Stonewall Peak.

Many of the grey tree "skeletons" are the remains of former pine species (Pinus ponderosa, Pinus jeffreyi and Pinus coulteri). In the foreground are different oak species (Quercus agrifolia, Quercus kelloggii and Quercus wislizeni) that coincidentally survived the fire. However, many oaks burned elsewhere on the mountain. 

Beneath the burned trees in the distance are various species of ceanothus, manzanitas and stands of chamise (Adenostoma fasciculatum). With the forested canopy now removed, these chaparral species are able to grow and spread throughout the exposed slopes. They become an important element of the fire recovery by covering exposed soils, replenishing soil nutrition, and serving as habitat for the native fauna.    

Cuyamaca Mountains, Winter of 2014 - View looking north towards from the Harvey Moore Trail.

Stands of Chamise (Adenostoma fasciculatum), Birch Leaf Mountain Mahogany (Cercocarpus betuloides var. betuloides), and Cupped Leaf Ceanothus (Ceanothus perplexans) grow into their former glory. Many grow 6' to 8' tall and create a tough thicket throughout much of the trail area. Stands of California Buckwheat (Eriogonum fasciculatum) now also thrive in this area were there was once a greater number of Coast Live Oaks (Quercus agrifolia). But to many, this successional landscape can unfortunately still look disturbed and bare.  

Cuyamaca Mountains, Winter of 2014 - View looking north towards Stonewall Peak with Middle Peak in the distance. 

In the foreground, non-native grasses now dominate the grassland habitats. Periodic fire events have undoubtedly shaped the landscape in many ways. Unfortunately, one way is through the invasion of non-native grasses. When all too frequent fire events occur, it makes it hard for the native vegetation to establish successional plant species needed to keep the ecological checks and balances in order. When areas burn multiple times within a relatively short window of time (<30 years), the fire frequency eliminates the establishment of slower growing native species and thus enables fast growing non-native grasses (including other invasive plants) to take hold. Over time, the non-natives displace the natives. 

The invasive non-native grasses and other invasive plants are primarily spread through human activity and then further accelerated by continued human disturbances. Management of invasive species is critical to sustaining a healthy native ecology. So is managing a fire interval in keeping with the ecology. The non-native grasses make it the harder to reduce reoccurring fires. The non-native grasses are annual grasses that die out in summer and are therefore very susceptible to ignition. Once ignited, they facilitate the spread of low burning ground fires that can then spread into other adjacent native habitats.    

Laguna Mountains, Winter of 2014

The Cedar Fire of 2003 also burned parts of the Laguna Mountains, where stands of Black Oaks (Quercus kelloggii) and Ponderosa Pines (Pinus ponderosa) were greatly impacted. 

Laguna Mountains, Winter of 2015 - Juvenile Coulter Pines (Pinus coulteri) 

Coulter Pines are one specie that recovers fairly well after a fire. The seeds can successfully germinate in the bare mineral soils and, like other pine species, the trees are known to take hot full sun conditions. As a result, stands of Coulter Pine typically come back after high severity fires. 

In addition to stands of mixed evergreen forests, the Peninsular Ranges are also abundantly covered in chaparral. Like most of southern California's mountains (& quite possibly like much of California), chaparral is the prevailing habitat type. It is a strong, efficient and robust habitat that is well adapted to re-occurring fire intervals. The vegetation in this habitat typically has sclerophyllous leaves with a waxy cuticle. The tough and waxy leaves help the plant retain water during a long and hot dry season. Species like Lemonade berry (Rhus integrifolia), Toyon (Heteromeles arbutifolia), and Chamise (Adenostoma fasciculatum) become signature plants in mid-elevation chaparral habitats. And those are just a few of the many shrubs that make chaparral their home. Chaparral habitats are diverse and biologically very important. Their coevolution with fire means they can (and will) periodically burn, but the burn is also what invigorates their successful establishment. The habitat just needs time to recover free from additional impacts and disturbances.  

Xylococcus bicolor (Mission Manzanita) in Pine Creek Valley on the south side of the Laguna Mountains. It's one of the so called gems of the southern California chaparral. For range information, see:

Mission Manzanita is a fairly rare plant limited to chaparral habitats in southern California and northern Baja. Despite its limited range, Mission Manzanita is still relatively easy to find when hiking through portions of San Diego County.   


The Cuyamaca and Laguna Mountains receive about 25" of rain per year. That is about twice the annual rainfall that falls along the San Diego coastline, just 40 miles west of the range. Owing to influences of elevation and adiabatic cooling, the mountains of east San Diego County receive enough moisture to host an amazing flora that is not widespread throughout southern California, including disjunct floral species far removed from their more usual northern latitudes. So what gives? How is it that these more northern aligned species persist in the mountains of east San Diego County?

The mountains of east San Diego County are fortunate to receive some trace of summer rain. While the remainder of coastal southern California receives virtually no rain during the summer months, the mountains of east San Diego County are known to receive at least a few inches of rain during the summer. 

Summer rain is significant in California. One of the key elements of California's Mediterranean climate are warm, dry summers. That means, for the most part, rainfall in California only occurs from late fall through early spring. In the remainder of the year California undergoes drought-like conditions. Many of the native plant species throughout southern California employ adaptive traits that enable their survival during warm and dry summers.  

The presence of summer rain is significant in California because it's generally the exception to a rule. In summer, monsoonal flows of moisture make their way up the Gulf of California. The warm, shallow waters of the Gulf of California pump moisture into the atmosphere and create a wonderful pattern of wet and warm storm cells that brush across the southwest. These rains bring a great reprieve to the arid southwest deserts and monsoon season drives much the desert ecology.

While the bulk of these monsoonal storms flow over the Sonoran Desert in Arizona, these storms occasionally reach into southeastern California. When they do, these monsoonal rains grace southern California with some warm season precipitation. The higher elevations of the Peninsular Ranges can get a few inches of supplemental summertime precipitation, which is enough to support Sugar Pines (Pinus lambertiana) through a long hot and dry season. It's a pretty cool experience to be sitting in the shade of a Sugar Pine  while staring out over the Anza Borrego Desert.

Sugar Pine (Pinus lambertiana) growing near the summit of Cuyamaca Peak. In the far distance are mountains out in the Anza-Borrego Desert State Park. Whale Peak is in the far right of the photo. 

The stand of Sugar Pines growing atop Cuyamaca Peak are one of the southernmost stands in California. The next southernmost stand occurs in the Parque Nacional Sierra San Pedro Mártir of Baja California (roughly 150 miles south of Cuyamaca Peak). Sugar Pines are far more common throughout the western slope of the Sierra Nevada mountains and the North Coast Ranges of northern California. But the higher elevations of the Cuyamaca, Laguna and Palomar Mountains receive enough precipitation to allow these Sugar Pines to persist. 

For range information, see:

West Slope of Palomar Mountain - View looking west

The west slope of Palomar Mountain is home to a number of different conifer species: White Fir (Abies concolor), Jeffrey Pines (Pinus jeffreyi), Sugar Pines (Pinus lambertiana), Yellow Pine (Pinus ponderosa), and Big Cone Spruce (Pseudotsuga macrocarpa). Palomar Mountain rises to 6,533 feet in elevation, making for a fairly sizeable uptick in precipitation when compared to the adjacent lower lying southern California coast.  

Mountain Dogwood (Cornus nuttallii) at Palomar Mountain. Like the Sugar Pines (Pinus lambertiana), Mountain Dogwood is far more common along the western slope of the Sierra Nevada and North Coast Ranges of northern California.

For range information, see:

Mountain Dogwood (Cornus nuttallii) at Palomar Mountain

Mixed Evergreen Forests at Palomar Mountain. This assemblage includes a mix of Oaks and Conifers. Species include Canyon Live Oak (Quercus chrysolepis), Black Oak (Quercus kelloggii), Coast Live Oaks (Quercus agrifolia), White Firs (Abies concolor), Sugar Pines (Pinus lambertiana), and a Bigleaf Maple (Acer macrophyllum) here and there. 

Big Laguna Lake in the Laguna Mountains

Around 11,000 years ago, the climate of California was going through a cold-wet cycle. It was a time within the Pleistocene. At that time, a mixed conifer forest grew along the coast and throughout the mountains of southern California. Redwoods grew as far south as Carpinteria and mixed coniferous forest were able to move down slope to the lower elevations of the Peninsular Range. By around 8,000 years ago, warm and dry conditions had returned to California. Sclerophyll vegetation was once again able to spread. Over time the sclerophyll vegetation displaced the patches of mixed coniferous forest that had moved downslope. During this warm-dry cycle, the mixed coniferous forests were forced to retreat to the higher elevations and mountain peaks of the Transverse Ranges and Peninsular Ranges. They have remained there ever since.     

Spring in the Laguna Mountains

Spring in the Laguna Mountains


View from the Laguna Mountains looking east over the San Felipe Valley.

The eastern escarpment of the Peninsular Ranges rapidly drops down into the hot and dry Sonoran Desert (or, more specifically, the Colorado Desert, which is a subset of the greater Sonoran Desert). To the east of the Cuyamaca and Laguna Mountains lies Anza Borrego State Park, a renowned desert  landscape.

Like the Sierra Nevada, the Peninsular Ranges act as a physical barrier that block westward moving winter storms. In the process, the mountains wring moisture out of those westward moving storms and cast a rain shadow over the lands that fall to the east. 

View looking southwest from the Palomar Mountains

While the eastern escarpment is steep and sharp, the western slopes of the Peninsular Ranges gradually descend via a series of foothills and mesas. The western slopes lie within the California Floristic Province (CFP), which is defined by a Mediterranean climate known for its maritime influence. The CFP is a temperate climate moderated by a moist air mass that blows off the Pacific Ocean. While the CFP is also known for its seasonal patterns of mild wet winters and warm dry summers, the temperate influences of the Pacific Ocean moderates the growing conditions and allows for an abundance of plant species. As such, the CFP hosts a spectacular diversity of plants and makes California a botanical hotspot. 

View looking east towards Anza Borrego State Parfrom the eastern escarpment of the Laguna Mountains 

In contrast to the western slopes, the eastern slopes of the Peninsular Ranges lie within a transition between the California Floristic Province to the west and the Sonoran Desert Floristic Province to the east. The difference between the two floristic provinces is marked by a shift from a temperate coastal influenced climate to a hot and dry continental climate. 

Continental climates are not moderated by oceanic influences and therefore lack the mitigating measures that regulate temperature extremes. Consequently, continental climates typically experience hot summers and cold winters. In the case of the Sonoran Desert, this distinction has resulted in a hot and arid desert ecosystem. That climatic difference shapes the desert ecology and has resulted in distinct lineages of plant species and floristic composition.

While the transition between the two floristic provinces may look stark, it actually occurs as a gradient with lots of nuances. Microclimates, pockets of moisture, air flow patterns, geology, and other edaphic features create a rich and robust matrix of change that gradually unfolds as you descend in elevation. The changes can be subtle or slight. Regardless, it a fascinating play of edaphic ecology. 

View looking west from the east side of Palomar Mountain - Elevation: ~4,000'

In the far distance is the east side of Mt. Palomar. As the eastern slopes of the Peninsular Ranges descend into the lower elevations, the conifers and mixed evergreen forests atop the mountain peaks and ridges start to thin out. Forest species then start to consolidate within the creeks and drainages, where year round moisture remains and temperatures are generally more cool.

At the ridgeline in the upper left foreground is a small stand of White Fir (Abies concolor) hugging the headwater of a creek. From there, the stand of White Fir transitions to oak woodland and chaparral, with chaparral especially dominant on the south facing slopes. Eventually, chaparral species cover much of the upper middle elevations. 

Southeast facing slope in the Laguna Mountains - Elevation: ~4,000'

Where precipitation starts of drop off due to the rain shadow effect, the precipitation patterns no longer supports Oaks and Pines. Instead, widely spaced shrubs and other drought tolerant vegetation takes over, including many signature chaparral species. Here, Manzanitas (Arctostaphylos spp.), Chamise (Adenostoma fasciculatum) and Chaparral yucca (Hesperoyucca whipplei) dot the hillside. 

NOTE: This area also burned during a past wildfire. You can see the Chamise (Adenostoma fasciculatum) re-sprouting from it's crown. 

Whether in flower or not, Chaparral yucca (Hesperoyucca whipplei) holds its own.

Ashy Silktassel (Garrya flavescens) growing amidst the Chaparral yucca (Hesperoyucca whipplei).

Parish's Rabbitbrush (Ericameria parishii) growing in the upper reaches of an east facing exposure within the Laguna Mountains - 

Elevation: ~5,000'

Along the east facing exposures of the higher ridgelines, the conditions can be both cold and dry due to both the montane elevation and a slight rain shadowing effect. Ericameria species can be great at sustaining cold, dry environments, like that of the east facing Laguna Mountain escarpment. 

Quite often the Peninsular Ranges rise in stark contrast to the semi-arid or arid landscape that surrounds the range. When that happens, an island effect takes place whereby the ecosystems throughout the upper elevations of the mountains are unique when compared to the surrounding terrain. This can result in isolated species, similar to those species growing on an island. The term 'sky island' is sometimes used to describe mountains that rise in contrast to a different lowland environment, much like the Peninsular Ranges do.

Species confined to such sky islands are limited in their ability to spread and disperse across the landscape due to a lack of suitable habitat and growing conditions throughout the lowland environment. As such, some of these isolated species undergo speciation events that effectively give birth to new species. And, as quite often happens, the isolated growing conditions results in a plant edging out an existence within a niche environment, which is a great recipe for producing rare plants. 

The Laguna Mountains Goldenbush (Ericameria cuneata var. macrocephala) is a rare plant found only within the Laguna Mountains. However, the parent specie, Cliff Goldenbush (Ericameria cuneata), remains widespread throughout California. Presumably, the unique growing conditions and/or isolation of the Laguna Mountains has lead to the birth of a subspecie - the rare Laguna Mountains Goldenbush (Ericameria cuneata var. macrocephala). 

Laguna Mountains Goldenbush (Ericameria cuneata var. macrocephala) in post flowering form.

Laguna Mountains Goldenbush (Ericameria cuneata var. macrocephala)

East facing slope of the Palomar Mountains - Elevation: ~3,000'

As the mountains descend into the desert floor, the habitat transitions from chaparral to desert scrub. Like much of the transition, the transition occurs as a gradient where chaparral species, like California buckwheat (Eriogonum fasciculatum var. polifolium) and Showy penstemon (Penstemon spectabilis), intermix with other high elevation desert species, like Pinyon Pines (Pinus monophylla). 

Desert Scrub - Elevation ~ 2,500'

As you descend in elevation, the conditions become significantly more hot and dry and the vegetative cover becomes more sparse. Sometimes this habitat is referred to as Desert Transition, where much the remaining chapparral species are limited to the more hot and dry adapted types. Here a notably dry adapted form of California Buckwheat, Eriogonum fasciculatum var. polifolium, is able to hold on in these desert-like conditions.

A jewel of the desert scrub: Mirabilis multiflora (Giant four o'clock) w/ California buckwheat.

Alas, vegetative cover gives way to an abundance of rock as the mountains descend into the desert. And a new floristic province firmly takes over.

A spring storm in the Laguna Mountains as seen from the desert.

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