Santa Margarita Ecological Reserve: South Gate to the Temecula Gorge

Trip Parameters
Trip Description
   Detailed Trip Log
Sources and Further Information


This is one of two commonly used docent tours for the Santa Margarita Ecological Reserve. The Reserve is only open to the public during prearranged tours with a docent. See Santa Margarita Ecological Reserve for more information.

This route allows a view of virtually the entire accessible Reserve, travelling from the southwest corner of the Reserve through its center to the jewel of the Temecula Gorge in the north part of the Reserve.

Docents meet tour participants in a working avocado and citrus research grove. Leaving behind the tropical orchards, the route descends into the shade of a live oak gallery forest along Stone Creek. The tour then rises into chaparral and coastal sage scrub and journeys along the San Diego Aqueduct northward before dropping suddenly and dramatically into Temecula Gorge and the cool riparian forests of the Santa Margarita River.

At the Gorge, the erosional forces of river water have dug deep into the granite of the rising Santa Ana Mountains. The Gorge clearly shows the erosion in progress, with steep immediate walls that are ~235' above the River, and with a total relief of ~828' in a distance of only 0.25 miles.

Trip Parameters

Maps: Route.

Season: October to June are the best months, but the hike can also be done in the early morning or late afternoon in July through September.

Trailhead and directions to trailhead: The south entrance of SMER. See directions at Santa Margarita Ecological Reserve.

Length: 6.5 miles roundtrip, 5.5 miles roundtrip using the shortcut (numbers accurate to ~0.1 mile).

Elevation Changes: 1400' gain and loss, 1430' using the shortcut (numbers accurate to ~20'). See Altitude Profile.

Users: Hikers or horseriders.

Route Condition: Dirt road in good shape.

Route Maintenance:


Trip Description

This description is in the format of the docent-led tour. The mileages below are accurate to ~0.1 mile, but are quoted to 0.01 mile in order to preserve the relative accuracy between points. Elevations are accurate to ~5', interpolating between 20' contours. See the Detailed Trip Log for an overview of the major points without the description provided here.

The hike starts at the Ranch House, now used as the headquarters for the Reserve. The Ranch House is surrounded by a working citrus and avocado orchard, which is managed by the East Brothers for the Reserve. Although the orchard is operated essentially normally, it is also used for research. One ongoing project is testing the effectiveness of the standard agricultural practice of bringing in honey bees to pollinate the crop. Two sizes of mesh bags are placed on flowers. One size allows only the smaller native bees to enter and pollinate the flower; the other size allows both in. This will allow a clean test as to what additional pollination benefits derive from the honey bees.

At mile 0.30, we leave the orchard and descend to Stone Creek. On the left is Diegan Coastal Sage Scrub, which contrasts markedly with the orchard. Although the orchard may look greener and more "productive", consider the kind of communities each supports. The orchard has essentially one main species, the avocado, and the orchard supports perhaps a very limited number of weed and insect species. In contrast, the Coastal Sage Scrub is richly varied in the visible plants, and equally as rich in the insect and animal community that lives there.

What do you think will happen to the native community of plants and animals if the entire habitat is planted to groves?

This is a good spot to survey the next part of the hike, and the plant communities that we will travel through:

The deep shade of trees along Stone Creek at mile 0.37 is cool and refreshing on a hot day. In addition to the visual delights of such a cool retreat away from the sun, the actual temperature is significantly cooler here due to transpiration. One oak tree can transpire 300 gallons of water per day! The plants of this riparian habitat don't need to be thrifty with their water consumption like their counterparts in the Coastal Sage Scrub and chaparral.

Note how much life is supported by this habitat. The streambed itself looks like a jungle in many places. Even the rock walls of the cliff support a variety of plants, including the fascinating mosses which can change from black to green in literally minutes when they get wet.

The trees in the watery habitat are short-lived, having an average life-span of ~35 years, and get longer-lived with increasing distance from the water. Willows have the shortest life span and can live in the water, sycamores live longer and are found farther from the center of the stream. Finally, on the stream banks and away from constant moisture, the live oaks can live for 300-400 years.

It is not surprising that such a rich variety of plants will find many species that have been used by humans. For example, the wild grapevine that grows in abundance here saved the wine industry in California in the 1870s and 1880s. The varieties of wine grown then could not resist phylloxera, a plant louse. But it was soon found that the native grapevine was resistant to the pest, and soon every grape plant grown in California was grown on roots of the wild grapevine such as those found here.

It is critical to preserve native species, not only for their own benefit but also for their potential use to humans in the future in the form of new drugs. For example, one of the leading anti-cancer drugs, taxol, was found in the bark of the Pacific yew tree. Who knows how many more drugs will be found in the vast number of species as yet unexplored for them?

At mile 0.7 the road diverges from the creek bed, and we emerge into the chaparral. The plants of the chaparral are truly amazing. They can survive and even thrive for nearly a year without water, managing to survive the hot dry summers using perhaps only the 5" of rain falling in a short rainy season. This ability needs to be bred into some of our garden plants, which may wilt without daily water!

The plants of the chaparral are not only survivors - they are beautiful in their season. The stunning blue or white California lilac is perhaps the best known of the plants of the hard chaparral, and produces beautiful displays in spring. The name for one variety reminds us why it is called hard chaparral: whitethorn ceanothus. Those thorns can literally tear your clothes to shreds if you must walk through significant patches of it.

California buckwheat is perhaps the best known member of the soft chaparral. Its soft white ubiquitous blooms appear in summer, age to golden brown and last until the new blooms appear the next year.

Amidst the larger members of the chaparral are a number of beautiful smaller flowers. One of the smallest, a belly flower since to see it best you almost need to be lying on your stomach, is rattlesnake weed, which forms a low mat about the width of your shoe and is covered by smiling little flowers. A taller flower, slender tarweed, can form masses of beautiful yellow flowers in the middle of summer, when it hasn't rained for months. Like many flowers that bloom in summer and fall, the leaves of tarweed are strongly scented, perhaps to discourage animals from browsing on the foliage to allow it to survive to bloom.

To see such beautiful flowers in later summer leaves one with an indelible impression that these plants are special, incredibly well adapted to their surroundings, and deserve to be preserved in their own right.

At mile 1.2 we enter a 5 acre inholding that predates the Reserve. Please respect the private property as we pass through it, and be alert for their dog! The young avocados on the left were planted in 2000.

At mile 1.4 we leave the inholding and turn left at the junction with the Aqueduct Road. We will largely follow the Aqueduct the rest of the trip.

There are two major pipelines buried 9-10' below the surface here, both of which originate at Lake Skinner and continue to the south portion of San Diego County. The water flows entirely by gravity along the entire route of the Aqueduct. San Diego #4, a 99" diameter pipe carrying 240,000 gallons per minute of treated water, was buried here along a 150-350' corridor. San Diego #5, a 72" diameter pipe carrying untreated water for agricultural use and also delivered to treatment plants, was buried here in 1983.

The story of these aqueducts is a fascinating one in itself, but I don't have space to describe it here. Two aspects of the aqueduct are clearly seen on this tour.

First, there are above-ground structures at every hill and valley along the way. At the top of hills, there are air-relief chambers to allow entrained air to escape from the pipeline. At the bottom of valleys, there are escape valves to allow the release of water if the pressure becomes too great, or to allow the aqueduct to be pumped out at that point if needed.

Second, the construction of the aqueduct inadvertently created an interesting scientific experiment. Essentially, the pipeline created a 150-350' cut completely through the heart of the Reserve. All native vegetation was removed, and the soil was completely disturbed to a depth of at least 10'. At the end of construction, the corridor was reseeded using both native and non-native (exotic) species. The major question this gives rise to is What happened next?

Naively, one would think that this would be a study of how the native community reestablishes itself. Instead, 12 years later, a study done by Thomas Zink et al in 1995 showed that the corridor is still distinctly different from the rest of the Reserve, and consists mostly of non-native plants! Worse, the corridor has served to be a base for the invasion of the rest of the Reserve for these exotic plants.

The corridor itself affects the Reserve through the continuing presence of the service road that we are on. Roads themselves fundamentally change an area. This isn't a surprise. Look out your front door and you immediately realize the threat that traffic on a road has to your children, and you don't allow them on the road until they are old enough to be careful. Animals and plants are also fundamentally affected by roads.

Many animals never learn road safety, and die simply due to the presence of roads. A huge mountain lion barrier had to be built on I-15 just east of here in order to prevent mountain lion deaths. Hundreds of toads are killed with every rainstorm on just one road in the Fallbrook area, the De Luz Road, since they actually come out to sit on the road and absorb the moisture that is easily available during and immediately after rains. Fortunately, since traffic on the roads in SMER is extremely light, this isn't a problem here.

However, other animals won't cross a road at all, and the road serves to fundamentally restrict their habitat. If the road creates too small a habitat, the animal will become extinct there. Much research is ongoing to quantify the effects of roads for various species.

At mile 1.8, we reach the split between the shortcut that follows the route of the aqueduct, and the continuation of the Red Mountain Truck Trail that we are on. This is also roughly the boundary between the Diegan Coastal Sage Scrub and the Southern Mixed Chaparral. We now see more of the hard chaparral, including California Lilac.

At mile 2.3 the road forks. On the right, the Red Mountain Truck Trail continues to the Rainbow Glen gate. We go left, on Via Tornado.

At mile 2.6 we cross a small drainage that contains the Coast Live Oak Woodland community, and meet up with the shortcut road, going right.

At mile 3.0 we reach almost the top of the Santa Margarita River bank. A short excursion from the road gives an overlook of the Temecula Gorge.

The Temecula Gorge is one of the most interesting geologic places in Fallbrook. We're standing at the southern end of the Santa Ana Mountains, but we are in just the beginning of the Peninsular Ranges, one of the largest geological units in western North America. The Peninsular Ranges extend from the north end of the Santa Anas to the tip of Baja California, and are essentially a continuation of the Sierra Nevada.

Like the Sierra Nevada, the Santa Anas have a steep east face, where the uplift is greatest, and a gentle westerly slope. We're standing on the east face, with the Elsinore Fault just to our east. The Gorge clearly shows the erosion in progress, with steep immediate walls that are ~235' above the River, and with a total relief of ~828' in a distance of only 0.25 miles. This uplift is the fundamental reason why the Temecula Gorge is here, and not elsewhere along the Santa Margarita River.

But exactly how did the gorge form? Look at the river here. The upstream creeks are flowing in basically a flat area. What in the world made the river decide to cross the crest of the Santa Ana Mountains here?

The simplest solution is that the River was here before the mountains were uplifted. In fact, we know that 8 million years ago, this area was flat, since the basalt flows of the Santa Rosa Plateau spread across a flat surface. It is quite likely that those basalts covered all of the Reserve 8 million years ago. At that time, the Santa Margarita River flowed to the ocean across a nearly flat surface.

As the Santa Anas began forming, probably about the same time that the San Andreas Fault became active some 5 million years ago, the River maintained its course, cutting through the Santa Anas like a knife through butter. Thus the river probably roughly maintained its present elevation in this area as the land continued to get higher. As the land rose, erosion increased, and the upper layers of rock, including the Santa Rosa Basalt, were stripped away.

See Geology of Temecula Gorge for more information.

Continuing on the road, we pass through a gate and descend to the Santa Margarita River at mile 3.3.

At the switchback in the road just before the bottom, note the level platform just to the east of the road. This is a remnant of the railroad that operated along the Santa Margarita River during 1880s (see Field Guide to Fallbrook: The Santa Margarita River). The railroad route was planned by engineers from the East who didn't realize the enormous variation in the flows of western rivers!

The riverbed here has been scoured to the bedrock in many places. Flooding has become more intense in recent years with the increased paving in the Temecula area. For example, the rains of 1993 were a 20 year event, but the flood it created on the Santa Margarita River was a 100 year event.

This is a good place to observe the geology of the area since the rocks are clearly visible. But ignore the large white splotches seen on many of the rocks. You might be excused for thinking that this "large bird" poop is some interesting intrusion in the rock! The probable source of the poop is herons.

The Santa Margarita River here separates two major rock groups. In fact, this boundary is a likely place for erosion to occur, and hence may very well have determined the location of the river here.

To the north is the Bedford Canyon formation, metamorphic rock about 175 million years old. The Bedford Canyon formation was formerly marine sedimentary rock that was buried deeply enough to recrystallize and lose much of its original characteristics. It now is largely slates, phyllites, quartzite, and a bit of marble here and there.

To the south is somewhat younger granitic rock, which was liquid or semisolid when the Bedford Canyon was being baked. This granitic rock is mostly Woodson Mountain granodiorite, with Bonsall tonalite and diorite in places.

The contrast between the rocks is easily seen from a distance. The darker Bedford Canyon formation weathers to smooth slopes, whereas the lighter granite weathers to boulder-littered slopes. Go to the fresh exposures of rock in the River bed and try to tell the difference!

Rivers aren't forever, and the Santa Margarita River is no exception. Those who know the area know that Pala Creek drains south to the San Luis Rey River from its headwater near the south end of the Pechanga Indian Reservation. If the Pala Creek continues to erode headward, it will eventually capture the Temecula and Murrieta Creeks and convert them to its tributaries. If that happens, the Santa Margarita River will be left literally high and dry, and the Temecula Gorge will become a wind gap in the Santa Ana Mountains as it now is allowed to rise with the rest of the Santa Anas.

Detailed Trip Log

The mileages below are accurate to ~0.1 mile, but are quoted to 0.01 mile in order to preserve the relative accuracy between points. Elevations are accurate to ~5', interpolating between 20' contours.

Miles From StartElevation (feet)Comments
0.00620Ranch house
0.30660Leave orchard
0.37580Jct. Stone Creek. Left.
0.70680Jct. Mining Claim Road; Leave Creek
1.21880Enter inholding; Jct. old Red Mtn. Truck Trail
1.38900Leave inholding; Jct. Aqueduct Road
1.761100Jct. old route on right that goes over the hill directly
1.821170Jct. old Red Mtn. Truck Trail
1.891170Jct. Aqueduct Road (shortcut) and Red Mtn. Truck Trail. Right.
2.261230Jct. Via Tornado and Red Mtn. Truck Trail to Rainbow Glen Road. Left.
2.601080Cross drainage
2.701040Jct. Aqueduct Road (shortcut) and Red Mtn. Truck Trail. Right
2.961010Cross drainage
3.30785Santa Margarita River
Route using shortcut, from the first shortcut junction
1.891170Jct. Aqueduct Road (shortcut) and Red Mtn. Truck Trail. Left
2.151040Jct. Aqueduct Road (shortcut) and Red Mtn. Truck Trail. Right.
2.411010Cross drainage
2.75785Santa Margarita River

Sources and Further Information

Much of the information presented above came from the San Diego State University Docent Training Class taught at SMER in June and July of 2000.

A Field Guide to Coastal Southern California, Robert P. Sharp, Kendall-Hunt, Iowa, 1978.

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Copyright © 2000-2001 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Last update: 5 November 2001.