97Introduction

3

Resource Significance

Photos (clockwise): 1. San Dimas Experimental Forest. United States Forest Service photo. 2. Walnut tree. NPS Photo. 3. 

Hiking, Angeles National Forest. NPS Photo. 4. Eaton Falls. Photo by Eric Lowenbach.
98 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 
Chapter 3: Resource Signifi cance National Signifi cance of the San Gabriel Watershed and Mountains Study Area 99

Chapter 3: Resource 

Signifi cance

Criteria for National Signifi cance 

The National Park Service (NPS) uses four basic 

criteria to evaluate the national signifi cance of 

proposed areas. These criteria, listed in the National 

Park Service Management Policies, state that a 

resource is nationally signifi cant if it meets all of the 

following conditions:

• It is an outstanding example of a particular type 

of resource

• It possesses exceptional value or quality in 

illustrating or interpreting the natural or cultural 

themes of our nation’s heritage

• It offers superlative opportunities for public 

enjoyment, or for scientifi c study

• It retains a high degree of integrity as a true, 

accurate, and relatively unspoiled example of a 

resource

The NPS evaluates national signifi cance for 

cultural resources by applying the national historic 

landmarks (NHL) criteria contained in 36 CFR Part 

65 (see Appendix E), in addition to the criteria 

above.

National Park Service professionals consult with 

subject matter experts, scholars, and scientists in 

determining whether a study area is nationally 

signifi cant. Natural and cultural resource 

experts and scholars, locally and within the NPS, 

contributed expertise, research and technical 

review of this statement of signifi cance. See 

Chapter 8, Consultation and Coordination for more 

information on subject matter experts and their role 

in this portion of the study process.

National Signifi cance of the 

San Gabriel Watershed and 

Mountains Study Area

The topographically and geographically 

diverse study area contains a mosaic of natural 

communities that span both coastal and desert 

ecological regions. Plant communities range 

from coastal sage scrub in the coastal valleys and 

foothills, to unique subalpine habitats high in the 

San Gabriel Mountains, to desert scrub and Joshua 

trees at the northern base of the mountains. The 

region has a long history of human use with a wide 

range of historical and archeological resources.

Due to extensive urbanization in the Los Angeles 

region, many native plant communities and their 

associated wildlife are now rare, threatened 

or endangered. The intersection of biological 

resources and urbanization has made the southern 

California coastal region the most-threatened 

biologically diverse area in the continental United 

States (California Department of Fish and Game 

2007). Southern California has been identifi ed as a 

“hotspot” for biodiversity due to the high diversity 

of imperiled species (Stein, Kutner and Adams 

2000). Archeological and historical resources have 

also been impacted by urbanization.

In 1973, the National Park Service conducted 

a comprehensive survey of natural history in 

California and identifi ed sites with national 

signifi cance that would be eligible for National 

Natural Landmark designation. This survey found 

that for areas in the Transverse and Peninsular 

Ranges, “Much of the mountainous areas lack 

intensive agriculture or dense urbanization, unlike 

the lowland valleys and fl oodplains of this area. 

These upland sites are in many cases the sole 

remnant of the pristine landscape (NPS 1973).” 

This statement remains true today. The signifi cant 

resources within the study area are concentrated 

in the San Gabriel Mountains and foothills and 

in undeveloped hillside areas such as the PuenteChino Hills.

Nationally Signifi cant Regions

The NPS determined that two regions of the 

study area are nationally signifi cant, the San 

Gabriel Mountains and the Puente-Chino Hills 

(See Map: Nationally Signifi cant Regions). These 

regions contain outstanding examples of geologic 

resources and native southern California ecological 

communities. The San Gabriel Mountains are also 

culturally rich, with a long history of human use. 

Nationally signifi cant cultural resources in the San 

Gabriel Mountains include the Mount Wilson 

Observatory and the San Dimas Experimental 

Forest. 

SAN GABRIEL MOUNTAINS

The San Gabriel Mountains and foothills are 

nationally signifi cant for their geologic resources, 

high biodiversity, dynamic river systems, and the 

long history of scientifi c study and discovery. 

Early conservation of the San Gabriel Mountains 

ensured that these areas were protected from 

the rapid development of the Los Angeles basin, 

which began in the late 19th century. The active 

mountain system has created scenic and unusual 

landscapes that support a high level of ecological 
100 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

diversity. Within a short distance, the mountains 

and foothills feature coastal, desert, montane and 

sub-alpine ecological communities. This diverse 

landscape provides habitat for an abundance of 

rare and endemic plants and wildlife. In addition, 

the San Gabriel Mountains contain signifi cant 

waterways and riparian areas, some of which are 

eligible Wild and Scenic River segments. Nationally 

signifi cant cultural resources include the San Dimas 

Experimental Forest, which contains some of the 

earliest and most comprehensively and continuously 

monitored research watersheds, and the Mount 

Wilson Observatory which includes large telescopes 

that were used in signifi cant astronomical 

discoveries.

PUENTE-CHINO HILLS

The Puente-Chino Hills contain rare native plant 

communities. Although this area is somewhat of 

an island of open space surrounded by urbanized 

areas, the Puente-Chino Hills and the Santa Ana 

Mountains to the southeast together encompass 

about 500,000 acres of wildlands containing 

signifi cant biological resources.

The remaining portions of the study area which 

contain highly urbanized communities were found 

not to be nationally signifi cant. These areas include 

urbanized areas of the San Gabriel Valley and the 

Los Angeles Coastal Plain. Although signifi cant 

natural and cultural resources are located within 

these urbanized areas, these resources are highly 

fragmented and surrounding development has, in 

many cases, negatively impacted their integrity. 

National Signifi cance Criteria 

The following analysis describes how the study area 

resources meet the national signifi cance criteria. 

More detailed information on study area resources 

and historical context can be found in Chapter 2, 

Resource Description.

San Gabriel Mountains

CRITERION 1: IT IS AN OUTSTANDING EXAMPLE 

OF A PARTICULAR TYPE OF RESOURCE.

Natural Resources

Mountain building and diverse geology. The 

San Gabriel Mountains present the greatest vertical 

elevation gain for the shortest horizontal distance 

from the ocean, when compared to anywhere else 

in the continental United States. These mountains 

owe their ruggedness to the fact that they are one 

of the most tectonically active mountain systems 

in the United States. Tectonic activity along the 

San Gabriel Mountains, Vincent’s Gap. NPS photo. 
Chapter 3: Resource Signifi cance National Signifi cance Criteria 101
102 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

San Andreas and other regional faults force the 

mountains to rise at a rate of as much as 2 inches 

a year. The San Gabriel Mountains thus provide an 

ideal setting to learn about mountain building and 

plate tectonics. Geologists have studied the San 

Gabriel Mountains for many years and continue 

to make new discoveries about the evolution of 

the San Andreas Fault and the Transverse Range 

province (Gumprecht 1999, McPhee 1989, Murphy 

1985, Powell 1993).

One of the most geologically diverse mountain 

ranges in southern California, the San Gabriel 

Mountains are comprised of rocks from all 

the major geologic eras as defi ned by the U.S. 

Geological Survey’s geologic time scale. This 

includes the most extensive, best-exposed and most 

completely studied exposures of several geologic 

formations: the San Gabriel Mountains anorthosite 

massif, the Mount Lowe plutonic suite, and Pelona 

schist (Carter 1982a and 1982b, Ehlig 1982, Powell 

2007a). 

The San Gabriel Mountains also contain some of 

the oldest rocks in California. Ancient Precambrian 

rocks in the San Gabriel Mountains include 

Mendenhall gneiss (1.045 billion years old), 

anorthosite and related rocks (1.02 billion years old) 

and augen gneiss (1.7 billion years old). Although 

these rocks are not as old as the 3.6 billion-year 

old Archean rocks of the Lake Superior region, 

they do form part of the Precambrian core of the 

North American continent. Rocks of this age are 

typically associated with what geologists refer to as 

the North American craton, the old nucleus of the 

North American continent. Ancient rocks associated 

with the North American craton are typically found 

throughout the Midwest and in the Colorado 

Plateau (areas of Utah, Colorado, Arizona and New 

Mexico where the craton has been uplifted) (Norris 

and Webb 1990, Powell 2007b, Lillie 2005).

Within the San Gabriel Mountains there are many 

striking landforms. One such area is the Devil’s 

Punchbowl, a magnifi cently exposed ridge of 

steeply tilted sandstone that was forced out of 

areas of older crystalline rocks by tectonic activity 

along the San Andreas rift zone. Tilted sandstone 

ridges and associated riparian areas create a highly 

scenic landscape. The Devil’s Punchbowl was 

identifi ed by two previous studies as a nationally 

signifi cant geological feature (NPS 1974 and 

NPS 1976). The latter study recommended it for 

designation as a National Natural Landmark. It 

was described as “an ideal place to ponder the 

importance of the regional faults and to view 

the San Gabriel Mountains (NPS 1976).” Devil’s 

Punchbowl is designated a “Special Interest Area” 

by the Angeles National Forest and is managed as a 

county park by the Los Angeles County Department 

of Parks and Recreation. 

Geologic activity in the San Gabriel Mountains 

creates dynamic disturbance regimes. As a result 

of signifi cant tectonic activity, mountain building 

and climate, ecological systems in the region 

have evolved to be dependent on disturbance 

dynamics associated with fi re, fl ooding and erosion. 

Specialized plant communities have adapted to 

these disturbance conditions. 

The U.S. Forest Service’s San Dimas Experimental 

Forest (SDEF) is an international leader in the 

study of dynamic disturbance regimes. Established 

in 1933, the SDEF is one of the fi rst U.S. Forest 

Service experimental forests established in the 

nation. Created as a natural laboratory to study fi re, 

hydrology, and other topics related to chaparral 

ecology, the SDEF maintains some of the earliest 

and most comprehensive records from continuously 

monitored experimental watersheds in the United 

States (Jones and Stokes 2004). In 1976, the 

United Nations Educational, Scientifi c and Cultural 

Organization’s (UNESCO) Man and the Biosphere 

Program recognized the SDEF as a “Biosphere 

Reserve.”

The SDEF’s technological innovations in watershed 

research include:

1. the development of rain gauges and rain gauge 

networks to accurately measure precipitation in 

steep terrain, 

2. the development of fl umes (San Dimas Flume) 

to measure and withstand debris-laden fl ows, 

3. the identifi cation of post-fi re soil conditions, 

and 

4. use of lysimeters, large rectangular planters 

used to measure the infl uence of different 

vegetation types on water transpiration, 

evaporation, and percolation.

High levels of biodiversity. The topographically 

and geographically diverse San Gabriel Mountains 

feature climatic variations and extreme changes in 

elevation that create conditions for a high level of 

biodiversity. The San Gabriel Mountains contain 

plant communities that span two ecological regions 

(ecoregions): the coastal Southwestern ecoregion 

(coastal areas from Santa Barbara County to San 

Diego County) and the Mojave Desert ecoregion. 

Plant communities range from coastal sage scrub 

in the foothills, to unique subalpine habitats high 

in the San Gabriel Mountains, to desert scrub and 

Joshua trees at the northern base of the mountains. 
 Chapter 3: Resource Signifi cance National Signifi cance Criteria 103

Visitors to the mountains can experience all of 

these distinct communities in a two-hour drive from 

the City of Los Angeles. 

The wide range of vegetation types in the San 

Gabriel Mountains provides habitat for 67 sensitive, 

rare, threatened or endangered plant species. 

Federally listed threatened (FT) or endangered (FE) 

plants include: Nevin’s barberry (Berberis nevinii)

(FE), slender-horned spinefl ower (Dodecahema 

leptoceras) (FE), Braunton’s milk-vetch (Astragalus 

brauntonii) (FE), thread-leaved brodiaea (Brodiaea 

fi lifolia) (FT), and California Orcutt grass (Orcuttia 

californica) (FE). 

High levels of wildlife diversity are also present 

in the San Gabriel Mountains. Four of the six 

life zones (areas with similar plant and animal 

communities) identifi ed for North America by 

Merriam are represented in the San Gabriel 

Mountains: Lower Sonoran, Upper Sonoran, 

Transition and Canadian. No single national park 

unit in the Southwestern and Mojave Desert 

ecoregions contains this level of diversity.

Federally listed threatened or endangered animals 

include the arroyo toad (Bufo californicus) (FE), 

least Bell’s vireo (Vireo bellii pusillus) (FE), mountain 

yellow-legged frog (Rana muscosa) (FT), unarmored 

threespine stickleback (Gasterosteus aculeatus 

williamsoni) (FE), California condor (Gymnogyps 

californianus) (FE), California red-legged frog (Rana 

aurora draytonii) (FE), coastal California gnatcatcher 

(Polioptila californica californica) (FT), desert 

tortoise (Gopherus agassizi) (FT), Santa Ana sucker 

(Catostomus santaanae) (FT) and southern willow 

fl ycatcher (Empidonax traillii extimus) (FE). Other 

signifi cant species in the San Gabriel Mountains 

include black bear, the mastiff bat, kit fox, bighorn 

sheep and mountain lions.

In a statewide comparison, the San Gabriel 

Mountains contain high levels of biodiversity. The 

California Department of Fish and Game has 

identifi ed 12 measures to compare biodiversity 

throughout the state. These measures include 

species rarity, richness and endemism. The San 

Gabriel Mountains have among the highest levels 

of biodiversity for 8 of the 12 measures identifi ed 

including: vegetation type richness, plant rarity, 

amphibian richness, reptile richness, bird richness 

(winter and summer), mammal richness and 

invertebrate rarity. Although not among the richest 

areas for native freshwater fi shes in the state, 

within the southern California region, the San 

Gabriel Mountains are among the richest areas for 

native freshwater fi shes (California Department of 

Fish and Game 2003). 

Photos (top to bottom): 1. San Gabriel Mountains. 

NPS photo. 2. San Dimas Experimental Forest 

Lysimeter construction. Photo by the United States 

Forest Service. 3. Santa Fe Dam Natural Area. NPS 

photo. 
104 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

The Angeles National Forest manages special 

designated areas, including research natural 

areas and special interest areas, for research 

and protection of outstanding examples of 

habitat types. The Fern Canyon Research Natural 

Area (RNA) was established to protect chamise 

(Adenostoma fasciculatum), chaparral, and 

canyon live oak (Quercus chrysolepis) woodland. 

This area also includes a unique relict stand of lowelevation ponderosa pine (Pinus ponderosa) at 

Brown’s Flat, a shallow 80-acre bowl created by an 

ancient land slump. Fern Canyon RNA falls entirely 

within the San Dimas Experimental Forest. Fern 

Canyon was affected by the 2002 Williams fi re but 

is expected to recover naturally (USFS 2005).

The Falls Canyon RNA encompasses a tributary of 

the West Fork of the San Gabriel River. This area 

was set aside to preserve rare stands of dense, 

mature bigcone Douglas-fi r trees, some of which 

are over 350 years old. Most old-growth, bigcone 

Douglas-fi r communities are in decline as younger 

trees do not survive well during the extreme fi re 

events common in the southern California. The Falls 

Canyon forest is more resistant to fi re because of 

its lack of understory vegetation. The U.S. Forest 

Service manages the Falls Canyon RNA to maintain 

biological diversity and provide ecological baseline 

information, education, and research.

Mount San Antonio and Mount Baden-Powell 

Special Interest Areas contain a rich array of isolated 

subalpine habitats close to large-scale arid and 

semi-arid landscapes. Mount San Antonio, the 

highest peak in the San Gabriel Mountains (10,064 

ft), contains rare alpine and subalpine plants, partly 

related to the local geology. The area supports an 

unusual subalpine forest of krummholz lodgepole 

pine, Pinus murrayana. Disjunct western juniper 

(Pinus occidentalis ssp. australis) also occurs here. 

Mount San Antonio is the only known locality in 

southern California for the rare dwarf hawksbeard 

(Crespis nana), an arctic-alpine plant species. Other 

rare plant species in this area include alumroot 

(Heuchera abramsii), bed straw (Galium parishii), 

and wooly mountain parsley (Oreonana vestita).

The area provides summer habitat for Nelson’s 

bighorn sheep, a California Species of Special 

Concern. Mount San Antonio was recommended 

as a potential National Natural Landmark in a 1979 

survey (NPS 1979, USFS 2005).

Mt. Baden-Powell, at 9,399 feet, features some of 

the best examples of 1,000 year-old limber pines in 

southern California. The peak and adjacent areas 

contain elements of subalpine habitat, including at 

least three endemic plant species (USFS 2005). 

Although pinyon-juniper communities are common 

in southern California, a community near Mescal 

Creek, which fl ows from the San Gabriel Mountains 

north to the Mojave Desert, contains an unusual 

relict/remnant juniper woodland. The type of 

vegetation found in this woodland is a remnant of 

vegetation that was prevalent in this area during 

the Pleistocene epoch (1.8 million to 8,000 years 

ago.) Fossils of similar juniper species associated 

with the Pleistocene epoch in Mescal Creek have 

been found in the La Brea Tar Pits in Los Angeles. 

Species include Juniperus californica and Juniperus 

utahensis. 

The Mescal Creek area juniper woodland was 

recommended for National Natural Landmark status 

in a previous study because of its high aesthetic 

value and the opportunity it provides to interpret 

the interaction of geologic history, plant geography, 

plant adaptation, water supply, desert-montane 

habitat and ecotones. 

No recent surveys of the Mescal Creek juniper 

woodland have been conducted. However, it 

remains an undeveloped area of the Angeles 

National Forest. There are few trails in the Mescal 

Creek Area and off-road vehicle use is not allowed. 

Dynamic River Systems. The highly erosive steep 

slopes of the San Gabriel Mountains produce 

dynamic river systems with rich habitat such as 

alluvial fan sage scrub and riparian areas. San 

Gabriel Mountains river segments that remain free 

fl owing meet eligibility criteria for Wild and Scenic 

River designation.

Alluvial Fan Sage Scrub. During rain events, water 

moves with great velocity from the mountains 

carrying soil and aggregate which are deposited in 

the foothills and valleys below. In years following 

fi re episodes, soils from slopes cleared of vegetation 

form mud and debris fl ows which can be highly 

destructive. Alluvial fan sage scrub is a specialized 

plant community that has adapted to this type of 

disturbance conditions. 

The study area contains some of the best remaining 

examples of alluvial fan sage scrub in the Los 

Angeles basin. Alluvial fan sage scrub is a distinct 

and rare plant community found on alluvial fans 

and fl oodplains along the southern base of the 

Transverse Ranges and portions of the Peninsular 

Ranges in southern California (Hanes et al 1989). 

Flood control projects, agriculture, and urban 

development have signifi cantly reduced alluvial 

fan sage scrub in river washes throughout the Los 

Angeles region (Davis et al. 1998). Only remnants 

of this habitat remain. 
 Chapter 3: Resource Signifi cance National Signifi cance Criteria 105

An analysis of ten stands of the most welldeveloped alluvial fan vegetation in Los Angeles, 

Riverside, and San Bernardino Counties found 

that Big Tujunga Wash is one of three sites which 

exhibits the most species diversity and the San 

Gabriel River is among one of two sites that exhibits 

the greatest structural diversity (Hanes et al. 1989). 

San Antonio Canyon and the upper Santa Clara 

River also contain excellent examples of alluvial fan 

sage scrub. 

Riparian Vegetation. A wide range of riparian 

habitats are present in the San Gabriel Mountains: 

Mojave riparian forest, southern coast live oak 

riparian forest, southern cottonwood willow 

riparian forest, southern mixed riparian forest, 

southern riparian scrub, and southern sycamore 

alder riparian woodland (Davis et al. 1998). These 

riparian areas support wildlife including threatened 

and endangered species such as the Santa Ana 

sucker, arroyo toad, unarmored threespine 

stickleback and the southwestern willow fl ycatcher.

Riparian areas are important for resident and 

migratory bird species. The Santa Fe Dam 

Recreation Area and the Santa Clara River at the 

base of the mountains contain riparian areas that 

are recognized International Bird Areas because 

they support a high number of bird species (Los 

Angeles County Department of Public Works 

2006a; Audubon Society 2007; San Gabriel 

and Lower Los Angeles Rivers and Mountains 

Conservancy 2001).

Wild and Scenic Rivers. Many river systems in 

the San Gabriel Mountains remain free-fl owing 

with intact riparian areas. The U.S. Forest Service 

determined, in its Angeles National Forest Plan, 

that free-fl owing stretches of the East, North and 

West Forks of the San Gabriel River and Little Rock 

Creek are eligible for National Wild and Scenic River 

designation (USFS 2005). 

Portions of these river systems traverse the San 

Gabriel and Sheep Mountain Wilderness Areas, 

providing opportunities for public enjoyment in a 

wilderness setting. The east and west forks of the 

San Gabriel River contain remarkable recreational 

East Fork San Gabriel River, NPS photo
106 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

values and provide easy access to year-round waterbased recreation. These river segments contain 

outstandingly remarkable scenic, recreation, fi sh, 

wildlife and historic resource values.

The Santa Clara River is the only major river corridor 

in southern California that runs freely without 

obstruction by major fl ood protection facilities. 

Although much of the upper Santa Clara watershed 

is located within the Angeles National Forest, the 

U.S. Forest Service did not include this corridor in 

their Wild and Scenic River analysis as the main 

stem of the river is outside the national forest 

boundaries. The upper Santa Clara River in the 

Soledad basin contains high quality riparian and 

aquatic habitats that support the Santa Ana sucker, 

arroyo toad, unarmored threespine stickleback and 

the southwestern willow-fl ycatcher. This area also 

functions as one of the important habitat linkages 

in the Los Angeles region, providing a connection 

between the San Gabriel Mountains and the Sierra 

Pelona Range (Stephenson and Calcarone 1999).

Cultural Resources

Scientifi c Research and Discovery. The San 

Gabriel Mountains have been the location for 

major scientifi c research and discovery. Nationally 

signifi cant research facilities within the San Gabriel 

Mountains that meet the criteria for designation 

as National Historic Landmarks include the 

Mount Wilson Observatory and the San Dimas 

Experimental Forest. 

Mount Wilson Observatory. A National Historical 

Landmark theme study for Astronomy and 

Astrophysics (1989) included a National Historic 

Landmark nomination for the Mount Wilson 

Observatory which establishes the signifi cance of 

the observatory. The Mount Wilson Observatory, 

established in 1904 by astronomer George Ellery 

Hale, contains fi ve major research telescopes still in 

operation. The 60-inch refl ector and the 100-inch 

Hooker refl ector made Mount Wilson the home 

of the two largest telescopes in the world in the 

early 1900s. These telescopes laid the technological 

foundation for all large modern telescopes. In 1981, 

the 100-inch Hooker refl ector was designated 

an International Historic Mechanical Engineering 

Landmark by the American Society of Mechanical 

Engineers (NPS 1989). 

Many of the major advances and greatest names 

in 20th-century astronomy are associated with 

the Mount Wilson Observatory, including Edwin P. 

Hubble and Albert Michelson. Astronomy questions, 

including the nature of sunspots, the temperature 

and composition of stars, and the structure and 

origin of the universe, were addressed by the 

greatest astronomers in the world using the best 

equipment at Mount Wilson (NPS 1989).

The observatory continues to provide opportunities 

for scientifi c study. The Center for High Angular 

Resolution Astronomy Array, operated by Georgia 

State University, is used for current astronomical 

research. It is the world’s largest optical 

interferometer array. University of California, 

Berkeley, operates the Infrared Spatial Inferometer.

San Dimas Experimental Forest. An “Inventory 

and Evaluation Report for the San Dimas 

Experimental Forest,” prepared by Jones and 

Stokes, concluded that the SDEF fi eld headquarters 

located in Tanbark Flats appears eligible for listing 

on the National Register as a historic district. 

The buildings and structures at the Tanbark Flats 

headquarters are excellent examples of Blanchard 

and Maher Forest Service Administration Buildings. 

Architects Blanchard and Maher designed the 

buildings to refl ect California’s architectural heritage Wild cactus in bloom. NPS Photo. 
 Chapter 3: Resource Signifi cance National Signifi cance Criteria 107

(wood buildings of the early days of the Mother 

Lode Country). Between 1933 and 1937, they 

produced over 200 designs. (Jones & Stokes 2004).

The SDEF facilities are among the earliest facilities 

constructed by U.S. labor programs during the 

1930s, including the Civilian Conservation Corps 

(CCC) and the Work Projects Administration labor 

programs, as well as a group of conscientious 

objectors (COs) assigned by the Civil Public Service 

program (Jones & Stokes 2004).

The Tanbark Flats fi eld headquarters appears eligible 

for listing on the National Register as a separate 

historic district. Research/ monitoring equipment 

includes a historical lysimeter facility (Jones & Stokes 

2004). The Lysimeter facility at SDEF (tunnel and 

instrument room) is the largest of its kind in the 

world. The facility contains 26 large lysimeters 

(each measuring 10.5 x 21 ft and 6 ft deep) and 

numerous small ones. The facility appears eligible 

for listing on the National Register as an individual 

resource and contributes to the larger historic 

district (Robinson 1985, Robinson 1991, and Jones 

& Stokes 2004). 

Other important CCC structures include stone 

landscape features (walls, stairs, fl umes, and 

walkways) that contribute to the cultural landscape. 

In total, the historic district includes 42 contributing 

resources. In addition, the natural features 

(topography, landscape) of the SDEF also contribute 

to the historic landscape setting (Jones & Stokes 

2004).

Potential Cultural Signifi cance. The Angeles 

National Forest contains several dams that are 

part of the comprehensive fl ood control system 

in the Los Angeles Region. The Los Angeles 

County Flood Control System is a comprehensive 

coordinated river-based fl ood-control system 

that was constructed by the Los Angeles County 

Flood Control District and the U.S. Army Corps of 

Engineers under the Flood Control Act of 1936. The 

Los Angeles County system was the fi rst and largest 

program to receive funding under this law. Because 

Mount Wilson Observatory 100-inch Hooker telescope. This image is reproduced by permission of The Huntington Library, 

San Marino, California.
108 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

of the geologic forces affecting the region extensive 

growth and development in the Los Angeles 

basin would not have been possible without the 

comprehensive fl ood control system. In addition to 

fl ood control dams, the system also includes other 

facilities such as debris basins, spreading grounds, 

diversion tunnels, outlets, inlets, guide walls, gates, 

and spillways.

In a recent theme study on large federal dams, 

the U.S. Bureau of Reclamation determined that 

the Los Angeles County Flood Control System 

might be nationally signifi cant for its impact on 

the history and development of the Los Angeles 

metropolitan region. Further study would be 

needed to identify which resources contribute 

to the national signifi cance of the system and 

to document the integrity of the contributing 

resources (Billington, Jackson, and Melosi 2005). A 

National Historic Landmark nomination would need 

to be prepared using the theme study guidelines 

for applying the NHL criteria to the fl ood control 

system. This nomination process would only happen 

if supported by the agencies that manage the fl ood 

control system facilities. 

Criterion 1 Conclusion

The San Gabriel Mountains provide outstanding 

examples of geologic resources, mountain building, 

native plant communities, wildlife, dynamic river 

systems, and cultural resources related to scientifi c 

research and discovery. The San Gabriel Mountains 

meet criterion 1.

CRITERION 2: IT POSSESSES EXCEPTIONAL 

VALUE OR QUALITY IN ILLUSTRATING OR 

INTERPRETING THE NATURAL OR CULTURAL 

THEMES OF OUR NATION’S HERITAGE.

Every unit of the National Park System preserves 

important aspects of our nation’s natural and/or 

cultural heritage. The National Park Service uses a 

series of natural and cultural themes to categorize 

the important resources protected by our national 

park units. The themes are used to evaluate 

whether resources in a study area would broaden 

and diversify resources protected by our national 

park system. 

The natural and cultural resources as described 

in the previous section possess exceptional value 

in illustrating the themes represented in the 

lists below. The Suitability chapter includes an 

evaluation of themes represented by resources 

in the study area in terms of their current 

representation in the national park system. 

Natural Themes

The geological and biological diversity of the San 

Gabriel Mountains are unparalleled in southern 

California. These resources represent the following 

NPS natural themes: 

Landforms of the Present. The “Landforms of 

the Present” theme describes the character of the 

landscape as a physical and scenic entity as it exists 

today, as well as present and past geologic events 

and processes. The following sub-themes related to 

Landforms of the Present are represented in the San 

Gabriel Mountains:

• Mountain Systems: The San Gabriel 

Mountains possess exceptional value in 

illustrating and interpreting mountain building 

and plate tectonics. 

• Sculpture of the Land: The Devil’s Punchbowl 

is an excellent example of sculpture of the 

land created by impressive geologic forces. 

This striking landform is a dramatic example of 

earth movement caused by plate tectonics.

• River Systems and Lakes: The East, West 

and North forks of the San Gabriel River, and 

Little Rock Creek are eligible for National Wild 

and Scenic River designation. They present 

an exceptional opportunity to illustrate free 

fl owing southern California river systems. 

The San Gabriel River system has played 

a signifi cant role in shaping the southern 

California region, both geologically and 

culturally.

Land Ecosystems. The theme “Land Ecosystems” 

represents vegetation types as well as the animal 

populations and physical environmental features 

which are often important elements in identifying 

and evaluating sites. The following sub-themes 

related to Land Ecosystems are represented in the 

study area:

• Chaparral (shrubs and evergreen forest 

trees): Coastal sage scrub, San Dimas 

Experimental Forest (chaparral)

• Dry Coniferous Forest: Bigcone Douglas-fi r, 

pinyon-juniper forest, subalpine forest

Land ecosystem themes represented by plant 

communities in the San Gabriel Mountains provide 

a unique opportunity to interpret native southern 

California habitats. Within a relatively short distance, 

visitors can experience excellent examples of coastal, 

desert, montane, alpine and subalpine habitats. 

The mountain habitat contains exceptionally high 

plant and animal diversity and representations of the 

vegetation types described above.
 Chapter 3: Resource Signifi cance National Signifi cance Criteria 109

Aquatic Ecosystems Themes. The theme 

“Aquatic Ecosystems” is based on geomorphic 

and other physical aspects of aquatic ecosystems. 

The sub-theme “Streams” represents aquatic 

ecosystems with fl owing waters. The following 

sub-themes related to Aquatic Ecosystems are 

represented in the study area:

• Streams: Some of the best remaining examples 

of alluvial fan sage scrub are located in the 

foothill canyons of San Gabriel Mountain 

rivers providing an exceptional opportunity 

to preserve and interpret rare remnants of 

southern California natural heritage. San 

Gabriel Mountain river systems contain 

high quality riparian habitat which support 

numerous rare, threatened, and endangered 

species. 

Cultural Themes

The San Gabriel Mountains contain historically 

signifi cant research facilities that represent the 

following cultural themes:

Expanding Science and Technology. This theme 

focuses on science, which is modern civilization’s 

way of organizing and conceptualizing knowledge 

about the world and the universe beyond. 

Technology is the application of human ingenuity 

to modifi cation of the environment in both modern 

and traditional cultures. Topics under this theme 

that are represented by nationally signifi cant 

resources within the study area include:

• Experimentation and Invention: Astronomy 

questions, including the nature of sunspots, 

the temperature and composition of stars, and 

the structure and origin of the universe were 

addressed by some of the greatest astronomers 

in the world using the telescopes and other 

equipment at the Mount Wilson Observatory. 

Research conducted at the San Dimas 

Experimental Forest has greatly contributed to 

our understanding of natural processes and 

chaparral ecosystems.

• Technological Applications: The telescopes 

at the Mount Wilson Observatory laid the 

technological foundation for all large modern 

telescopes. Major accomplishments and 

effects of research at San Dimas include the 

development of rain gauges and rain-gauge 

networks to accurately measure precipitation 

in steep terrain, the development of fl umes 

to measure and withstand debris-laden 

fl ows, and the identifi cation of post-fi re soil 

non-wet-ability.

• Scientifi c Thought and Theory: Research 

efforts at the Mount Wilson Observatory 

and the San Dimas Experimental Forest have 

shaped current scientifi c thought and theory 

in the areas of astronomy and Mediterranean 

watersheds and ecosystems.

Expressing Cultural Values. The theme 

“expressing cultural values” covers expressions of 

culture – people’s beliefs about themselves and the 

world they inhabit. This theme also encompasses 

the ways that people communicate their moral 

and aesthetic values. Topics under this theme that 

are represented by nationally signifi cant resources 

within the study area include: 

• Architecture: San Dimas Experimental 

Forest buildings and structures at Tanbark 

Flats are excellent examples of Forest Service 

Administration Buildings refl ecting California’s 

architectural heritage (wooden buildings of 

the early days of the Mother Lode Country). 

The buildings were some of the fi rst to be 

constructed by federal relief programs such as 

the CCC.

Criterion 2 Conclusion

The San Gabriel Mountains possess exceptional 

quality in illustrating or interpreting natural and 

cultural themes of our nation’s heritage, including: 

mountain systems, sculpture of the land, river 

systems and lakes, chaparral and dry coniferous 

forest, streams, expanding science and technology, 

and expressing cultural values. The San Gabriel 

Mountains meet criterion 2.

CRITERION 3: IT OFFERS SUPERLATIVE 

OPPORTUNITIES FOR PUBLIC ENJOYMENT, OR 

FOR SCIENTIFIC STUDY.

Scientifi c Study. Scientifi c study of geological 

features in the San Gabriel Mountains continues to 

provide major contributions to our understanding 

of plate tectonics. The Mount Wilson Observatory 

provides opportunities for scientifi c study in the 

fi eld of astronomy. Several guest institutions use the 

observatory.

The San Dimas Experimental Forest provides 

excellent opportunities for the scientifi c study of 

mountain watersheds and chaparral ecosystems. 

Studies completed at the experimental forest have 

greatly contributed to our understanding of natural 

processes and chaparral ecosystems. Technological 

innovations developed at the experimental forest 

to monitor watersheds are in use in similarly diverse 

areas all over the world.

The U.S. Forest Service manages the Falls Canyon 
110 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

and Fern Canyon Research Natural Areas to 

maintain biological diversity and provide ecological 

baseline information, education, and research. 

Mount San Antonio and Mount Baden-Powell 

Special Interest Areas provide opportunities to 

observe subalpine forest close to both desert and 

coastal environments. 

Proximity to the Los Angeles Metropolitan Area 

provides many universities and colleges alike 

with readily available access to the mountains for 

research.

Opportunities for Public Enjoyment. A scenic 

backdrop of the Los Angeles region, the San Gabriel 

Mountains offer dramatic views of both the coast 

and the desert. Over 15 million people live within 

a 90-minute drive to the San Gabriel Mountains. 

The Angeles National Forest, which includes the 

San Gabriel and Sierra Pelona Mountains, comprises 

70% of the open space in Los Angeles County. 

The Angeles National Forest describes itself as a 

“backyard wildland,” as local and regional families 

consider the forest a preferred destination for day 

use recreation. 

With over 3.5 million annual visitors, the Angeles 

National Forest is one of the most visited forests 

in the nation. Because of the steepness of the San 

Gabriel Mountains, visitation is highly concentrated 

along several prominent canyons such as Big 

Tujunga and San Gabriel canyons (USFS 2003a and 

2009).

Many recreation facilities constructed by the Civilian 

Conservation Corps (CCC) are among the fi rst of 

such facilities in the nation. The Angeles National 

Forest maintains historical trails, camps, and other 

recreation facilities that continue to serve millions 

of visitors each year. These facilities are being 

evaluated for listing on the National Register of 

Historic Places.

The Mount Lowe Railway Historic District in the 

Angeles National Forest was part of Los Angeles’s 

once active Pacifi c Electric Railway. When in 

operation, the railway included various stops within 

easy walking distances of mountain trail heads. 

Although only remnants of the railway remain 

today, there are opportunities to hike and learn 

about the railway from interpretive features.

Today, recreational opportunities in the San Gabriel 

Mountains include hiking, backpacking, climbing, 

camping, swimming, picnicking, birding, fi shing, 

off-highway vehicle driving, and horseback riding. 

The Angeles Crest Scenic Highway is the only 

developed road that traverses the San Gabriel 

Mountains from north to south. This road is an 

important access point for visitors to the national 

forest. The road offers unparalleled views and 

scenery.

The San Gabriel Mountains contain 5 nationally 

designated recreation trails. The Pacifi c Crest 

National Scenic Trail, which spans 2,650 miles from 

Mexico to Canada, traverses the mountain divide. 

Four national recreation trails also traverse the San 

Gabriel Mountains; the Gabrieleno Trail, the High 

Desert Trail, the Silver Moccasin Trail, and the West 

Fork (San Gabriel River) Trail.

Water-based recreation is one of the most popular 

activities in the forest. Visitors are drawn to the 

wild and scenic rivers that contain fl owing water 

throughout the year. Balancing recreation demand 

with the sensitive nature of these river systems is 

one of the major management challenges of the 

Angeles National Forest. 

The dynamic river systems that run through the 

San Gabriel and Sheep Mountain Wilderness Areas 

provide opportunities for public enjoyment in a 

wilderness setting. The east and west forks of the 

San Gabriel River contain remarkable recreational 

values and provide easy access to year-around 

water-based recreation.

Mount Wilson Observatory has allowed public 

visitation to its facilities since the 1930s. The 

museum interprets the astronomical knowledge. 

Nearby Skyline Park Picnic Area, operated by the 

U.S. Forest Service, is open to the public. The 

Mount Wilson Observatory Association provides 

walking tours on weekends and holidays. The 

Mount Wilson Trail provides additional recreation 

opportunities (Mount Wilson Observatory 2007). 

Criterion 3 Conclusion

The San Gabriel Mountains offer superlative 

opportunities for public enjoyment and scientifi c 

study. Over 15 million people live within a 90-

minute drive to the San Gabriel Mountains. The 

mountains have a long history of research in 

geology, Mediterranean ecosystems and astronomy. 

The San Gabriel Mountains meet criterion 3.
Chapter 3: Resource Signifi cance National Signifi cance Criteria 111

CRITERION 4: IT RETAINS A HIGH DEGREE 

OF INTEGRITY AS A TRUE, ACCURATE, AND 

RELATIVELY UNSPOILED EXAMPLE OF A 

RESOURCE.

The Angeles National Forest was part of an early 

conservation movement to protect wilderness lands 

and watersheds in California. It is one of the fi rst 

national forests in the United States and is the fi rst in 

the State of California. California has designated the 

Angeles National Forest a state historic landmark. 

Early conservation of the San Gabriel Mountains in 

1891 has largely preserved its natural and scenic 

integrity. Although certain areas of the mountains 

have been altered for fl ood control and recreational 

facilities, as a whole, the native plant communities 

and river systems remain intact and provide a refuge 

for wildlife. Areas with signifi cant resources retain a 

high degree of integrity and are relatively unspoiled 

examples of their type of resource.

With over 90% of the San Gabriel Mountains slopes 

being steep and rugged, much of the landscape 

has retained its natural character. Over one-quarter 

of the national forest lands within the study area, 

114,000 acres, are designated wilderness areas (USFS 

2005 and 2011). The Angeles National Forest has 

nearly 60,000 acres of inventoried roadless areas 

within the study area. Several conservation groups 

and members of Congress have proposed that some 

of these roadless inventory areas be designated 

wilderness. 

Nearly 20,000 acres of land in the San Gabriel 

Mountains are U.S. Forest Service special designated 

areas (research natural areas, experimental forests 

and special interest areas). As described under 

Criterion 1, these areas are protected for their 

botanical, geological, and research values.

Rare opportunities to see free fl owing rivers with 

perennial fl ows are available in the study area. The 

rivers are the main attractions of the national forest. 

The rivers are also home to several native fi sh species. 

The 2010 Station Fire has had impacts on some of 

the signifi cant resources as described previously 

in the Fire Effects section in Chapter 2, Resource 

Description. Habitat for threatened and endangered 

species has been damaged. Those species that reside 

in pools and riparian areas are threatened by erosion 

and debris fl ows. Recovery efforts have salvaged 

many of these species and habitat in many areas is 

recovering well due to weather patterns and efforts 

to control non-native species invasion. Additionally, 

those habitats that fared best in the fi re were those 

that were mature and had a high level of integrity. 

Continued restoration efforts on the part of the U.S. 

Forest Service will help restore habitats. One of the 

largest threats is the spread of non-native species. 

Forest closures and weed removal efforts are planned 

to reduce the spread of such species (USFS 2010).

The privately-owned Mount Wilson Observatory 

continues to operate on a renewed 99-year lease 

with the U.S. Forest Service. The observatory retains 

San Gabriel Mountains alluvial fan near La Crescenta. Photo by Jeremiah Easter.
112 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

a high degree of integrity of location, design, 

setting, materials, and association to their period 

of signifi cance. All fi ve signifi cant telescopes are 

still in operation and are in their original location. 

The natural setting of the Angeles National Forest 

contributes to the integrity of the observatory’s 

setting and association of the historic period 

(1904-present).

The design and setting of the observatory has been 

changed from the time the NHL nomination was 

prepared. New facilities added to the observatory 

are directly associated with the observatory’s 

purpose for astronomical research.

The San Dimas Experimental Forest historic district 

retains a high degree of integrity of location, 

design, setting, materials, workmanship, feeling, 

and association to their period of signifi cance. Many 

of the original CCC structures built for the SDEF 

remain. None of the resources have been moved 

and none has been greatly altered from its original 

design. Some resources are in a state of disrepair 

but all retain the majority of their original materials. 

Some minor alterations either occurred within the 

period of signifi cance or are so minor that they 

do not affect the overall integrity of the buildings 

(Jones & Stokes, 2004). 

The Williams fi re in 2002 destroyed 4 buildings 

within the Tanbark Flat headquarters area. The 

most signifi cant structure that was burned was the 

CCC Bunkhouse. It was a wood frame building that 

spanned Tanbark Creek much like a covered bridge 

(Jones & Stokes 2004). The SDEF retains the feeling 

and association of its historic period. 

Criterion 4 Conclusion

The San Gabriel Mountains retain a high degree of 

integrity and contain relatively unspoiled examples 

of signifi cant resources, despite impacts in some 

areas from reservoirs, utilities, roads, fi re, and 

recreational use. The San Gabriel Mountains meet 

criterion 4.

OVERALL CONCLUSIONS 

The San Gabriel Mountains meet all four criteria for 

national signifi cance:

• The San Gabriel Mountains provide outstanding 

examples of geologic resources, mountain 

building, native plant communities, wildlife, 

dynamic river systems, and cultural resources 

related to scientifi c research, and discovery.

• The San Gabriel Mountains possess exceptional 

quality in illustrating or interpreting natural 

and cultural themes of our nation’s heritage, 

including: mountain systems, sculpture of the 

land, river systems and lakes, chaparral and dry 

coniferous forest, streams, expanding science 

and technology, and expressing cultural values.

• The San Gabriel Mountains offer superlative 

opportunities for public enjoyment and 

scientifi c study. Over 15 million people live 

Puente Hills with a view of the San Gabriel Mountains beyond. NPS photo. 
Chapter 3: Resource Signifi cance National Signifi cance Criteria 113

within a 90-minute drive to the San Gabriel 

Mountains. The mountains have a long 

history of research in geology, Mediterranean 

ecosystems, and astronomy.

• The San Gabriel Mountains retain a high degree 

of integrity and contain relatively unspoiled 

examples of signifi cant resources, despite 

impacts in some areas from reservoirs, utilities, 

fi re, roads, and recreational use.

Puente-Chino Hills

CRITERION 1: IT IS AN OUTSTANDING EXAMPLE 

OF A PARTICULAR TYPE OF RESOURCE.

Natural Resources

High levels of biodiversity. The Puente-Chino Hills 

in the Los Angeles basin contain a diversity of native 

plant communities. Although this area is somewhat 

of an island of open space within urbanized areas, 

the Puente Hills along with the Chino Hills and the 

Santa Ana Mountains to the southeast together 

encompass over 500,000 acres of wildlands 

containing signifi cant biological resources (Noss, 

Beir and Shaw n.d.). Covering over 40,000 acres 

within the study area, the Puente-Chino Hills are 

an important component of this regional wildlife 

corridor (Puente Hills Landfi ll Native Habitat 

Authority 2007). This mountain system is associated 

with the active Whittier-Elsinore fault system. 

Maintaining this contiguous corridor is a high 

priority for state and local conservation agencies. 

“When combined with other habitat types in 

the area, such as chaparral and oak/sycamore 

woodland, the vegetation provides habitat for a 

unique assemblage of plants and animals” (Puente 

Hills Landfi ll Native Habitat Preservation Authority 

2007).

Despite its proximity to millions of people, the 

Puente-Chino Hills contain over 300 species of 

birds, deer herds, predators such as bobcats 

and coyotes, and one of the most diverse raptor 

populations in southern California. Twentytwo raptor species have been observed in the 

Puente-Chino Hills. Many of these species rely on 

connections to the larger regional corridor (Puente 

Hills Landfi ll Native Habitat Authority 2007). 

Within the study area, the Puente-Chino Hills 

provide habitat for sensitive, rare, threatened or 

endangered species. Federally listed threatened or 

endangered plants and animals include Braunton’s 

milk vetch (Astragalus leucolobus), least Bell’s 

vireo (Vireo bellii pusillus) (FE), southwestern 

willow fl ycatcher (Empidonax traillii extimus) and 

coastal California gnatcatcher (Polioptila californica 

californica). The U.S. Fish and Wildlife Service has 

designated much of the Puente-Chino Hills as 

critical habitat for the California coastal gnatcatcher 

(Puente Hills Landfi ll Native Habitat Authority 2007, 

CDFG 2006, USFWS 2007, Scott and Cooper 1999).

Most of the Los Angeles basin’s native plant 

communities have been destroyed by development. 

California walnut. Photo courtesy of BonTerra Consulting. 
114 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

However, excellent examples of coastal sage scrub 

and California walnut woodlands remain in the 

Puente-Chino Hills. Coastal sage scrub is one of the 

most threatened plant communities in California. 

Since 1945, the majority of coastal sage scrub 

vegetation in California has been lost to urban and 

agricultural land use (Kirkpatrick and Hutchinson 

1980). Only 15% of coastal sage scrub’s historic 

range remains in southern California. This habitat 

is of the highest priority for preservation (Davis et 

al. 1998, Mistretta 2007, personal communication, 

NPS 1973).

The Puente-Chino Hills are a transitional area 

for Venturan to Diegan coastal sage scrub 

communities. The California Natural Community 

Conservation Program identifi ed the PuenteChino Hills as a functioning biological unit of high 

conservation value for coastal sage scrub ( Puente 

Hills Landfi ll Native Habitat Preservation Authority 

2007, CDFG 1993).

California walnut (Juglans californica) woodlands 

and forests are found only in southern California. 

The historic distribution of California walnut 

woodlands and forests is limited to the areas 

between the Santa Clara River drainage in Ventura 

County on the north and the Chino Hills on the 

south. Outside this range, walnuts only occur 

interspersed with other foothill woodland species 

such as oaks (Quinn 1990). 

Contiguous stands of walnut woodlands and 

forests once lined the Puente-Chino and San Jose 

Hills, favoring shale soils that have a high waterholding capacity. Walnut woodlands and forests 

provide habitat for deer, nesting birds, and rodents. 

Today, California walnut woodland communities are 

in decline and residual stands are extremely limited. 

According to the California Natural Diversity 

Database (CNDDB), walnut forests are only found 

in small areas of Ventura and Los Angeles Counties. 

The best remaining stands of California walnutdominated forests and woodlands south of Ventura 

County are located in the San Jose and PuenteChino Hills. These stands have adapted to their 

local site characteristics and differ from the Ventura 

County stands in morphology and canopy structure 

(Quinn 1990). 

The CNDDB has on record approximately 17,000 

acres of remaining California walnut woodlands 

and forests. Approximately 2,300 acres are located 

in the study area. Only a small percentage (8%) of 

the California walnut woodlands and forests within 

the study area are in public ownership (CDFG 

2006). Some of the prime examples are currently in 

private ownership. (Quinn 1990).

In 1973, a National Park Service study identifi ed a 

grove of walnut woodlands in Diamond Bar as a 

potential National Natural Landmark (NPS 1973). 

Although this particular woodland has been 

reduced somewhat by development, woodlands 

and forests in nearby Brea and Tonner Canyons 

remain outstanding examples of walnut woodlands 

(Quinn 1990; PCR Services Corporation 2006).

Native walnut trees played an important role 

in the history of the region. During the 1900s, 

walnut production was almost entirely from 

Southern California. Success was due in part to 

use of the native walnuts to hybridize commercial 

walnut trees. Hybridization with native walnut 

trees improved the walnut’s resistance to heat. 

The Paradox Hybrid Walnut Tree in Whittier, a 

state historical landmark, was planted in 1907 by 

the University of California. This landmark tree 

represents the once fl ourishing walnut industry in 

Southern California.

Wildlife within the Puente Hills is diverse and 

abundant due to the large acreage of natural open 

space, the habitat types, and regional connectivity. 

While a few wildlife species are entirely dependent 

on a single vegetative community, the entire mosaic 

of all the vegetation communities within the area 

and connected areas constitutes a functional 

ecosystem for a wide variety of wildlife species. 

This includes areas both within the Puente Hills 

as well as the regional ecosystem. Habitat in the 

Puente Hills supports migrating large mammals, 

over-wintering birds of prey and nesting songbirds, 

including the California gnatcatcher (PCR Services 

Corp. 2006).

Cultural Resources

Although there appear to be no nationally 

signifi cant cultural resources in the Puente Chino 

Hills, the natural landscape contributes to the 

signifi cance of the Juan Bautista de Anza National 

Historic Trail and the Old Spanish National Historic 

Trail. The Puente Hills also contain numerous 

cultural resources of state and local signifi cances 

representing the Spanish/Mexican Rancho Period 

and historic oil industry sites.

Criterion 1 Conclusion

The Puente-Chino hills contain a high level 

of biodiversity and outstanding examples of 

southern California communities including coastal 

sage scrub, one of the most endangered plant 

communities in California, and the best remaining 

stands of California walnut-dominated forests and 
Chapter 3: Resource Signifi cance National Signifi cance Criteria 115

woodlands in their southern limit of distribution. 

The Puente-Chino Hills meet criterion 1.

CRITERION 2: IT POSSESSES EXCEPTIONAL 

VALUE OR QUALITY IN ILLUSTRATING OR 

INTERPRETING THE NATURAL OR CULTURAL 

THEMES OF OUR NATION’S HERITAGE.

Land Ecosystems Themes

The Puente Hills resources possess exceptional value 

in illustrating NPS natural history themes. Chapter 

4, Suitability, includes an evaluation of themes 

represented by resources in the study area in terms 

of their current representation in the National Park 

System. 

The following sub-themes related to Land 

Ecosystems are represented in the Puente-Chino 

Hills:

• Chaparral: The Puente-Chino Hills contain 

exceptional examples of coastal sage scrub. A 

unique transition zone between northern and 

southern affi nities, coastal sage scrub in the 

Puente-Chino Hills provides habitat for rare, 

threatened, and endangered species.

• Dry Coniferous Forest: The Puente-Chino Hills 

contain some of the best remaining examples 

of California walnut woodlands, a rare, 

endemic plant community.

Criterion 2 Conclusion

The Puente-Chino Hills possess exceptional quality 

in illustrating and interpreting natural themes of 

our nation’s heritage, including: chaparral and dry 

coniferous forest. The Puente-Chino Hills meet 

criterion 2.

CRITERION 3: IT OFFERS SUPERLATIVE 

OPPORTUNITIES FOR PUBLIC ENJOYMENT, OR 

FOR SCIENTIFIC STUDY.

Opportunities for Public Enjoyment

Easily accessible to the millions of residents that 

surround them, the Puente-Chino Hills feature 

several thousand acres of parks and open space, 

and miles of local and regional trails. Recreational 

opportunities include hiking, biking, horseback 

riding, and birding. A recreational route of the Juan 

Bautista de Anza National Historic Trail follows the 

popular Skyline Trail which traverses the PuenteChino Hills. Publicly owned and accessible stands of 

coastal sage scrub, walnut woodlands and forests 

can be found in Walnut Park, and the Puente Hills 

Landfi ll Native Habitat Preserve (Preserve). 

The largest area of preserved open space in this 

region of the study area is the Preserve. The 

Preserve offers superlative public enjoyment 

opportunities. In addition to traditional recreational 

activities such as hiking, jogging, mountain biking, 

and nature appreciation, the Preserve offers 

interpretation and outdoor education programs. 

Educational programs have included a Junior 

Ranger Program, guided hikes, campfi re talks and 

lecture series. Interpretive panels, kiosks and signs 

describe wildlife, vegetation, historical descriptions, 

and public safety information.

Scientifi c Study

The Puente-Chino Hills have been studied by 

numerous universities and conservation agencies. 

The Habitat Authority’s management plan 

encourages more opportunities for university-level 

research at the Preserve that would help to answer 

fundamental management questions regarding 

habitat and species of interest (Puente Hills Landfi ll 

Native Habitat Authority 2007). 

The California Department of Fish and Game 

defi ned portions of the Puente-Chino Hills as 

a recovery and research area for the Natural 

Communities Conservation Planning (NCCP) 

program. The NCCP Program was initiated in 1991, 

and is administered by the California Department 

of Fish and Game. The focus of this program 

is the coastal sage scrub habitat of Southern 

California, home to the California gnatcatcher and 

approximately 100 other potentially threatened 

or endangered species. The Orange County 

portion of the Puente-Chino Hills is included in 

the Orange County Northern NCCP subregion. 

Recently Chevron set aside a 28-acre preserve as 

part of a permit to complete oil fi eld abandonment 

operations in the area (California Department of 

Fish and Game 2008b).

Criterion 3 Conclusion

The Puente-Chino Hills feature public open spaces 

and miles of trails that provide opportunities such as 

hiking, biking, horseback riding, outdoor education 

and birding. Excellent opportunities are available 

for scientifi c research of native habitats and wildlife. 

The Puente-Chino Hills meet criterion 3.

CRITERION 4: IT RETAINS A HIGH DEGREE 

OF INTEGRITY AS A TRUE, ACCURATE, AND 

RELATIVELY UNSPOILED EXAMPLE OF A 

RESOURCE.

The Puente-Chino Hills have remained largely 

undeveloped despite the dense development that 

has occurred in the surrounding valleys and coastal 

plain. Lands in this hill system were historically used 
116 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

for oil extraction, grazing, and recreation.

Despite its long history of use and proximity to 

urban development, the Puente-Chino Hills support 

many of southern California’s native landscapes 

and sustain important habitat for numerous native 

animal species. Almost 17,000 acres of contiguous 

undeveloped open space within these hills contain 

signifi cant native habitat. The Habitat Authority 

manages almost 4,000 acres in the western PuenteChino Hills. The primary management objective is 

to protect biological diversity (Puente Hills Landfi ll 

Native Habitat Preservation Authority 2007). Large 

areas of undeveloped, privately owned land in 

the eastern Puente-Chino Hills contain some of 

the most signifi cant natural resources and provide 

key linkages and connections to the larger wildlife 

corridor. 

The slope, aspect and soil conditions of the PuenteChino Hills favor walnut woodlands and forests. 

Signifi cant contiguous stands line portions of the 

Puente-Chino Hills. These stands still retain the 

general pattern of walnut woodlands and forests 

documented over 50 years ago (Quinn 1990). 

Plant communities found within the Puente-Chino 

Hills are becoming increasingly rare on a global 

scale, as are many of the wildlife and rare plant 

species. These species require walnut woodland, 

oak woodland, chaparral, native grassland, and 

coastal sage scrub habitats contained in the PuenteChino Hills (Puente Hills Landfi ll Native Habitat 

Authority 2007). 

“Biologically, this area preserves a microcosm 

of the California Floristic Province, an identifi ed 

biodiversity hot spot in North America and a genetic 

reserve for the continent (Puente Hills Landfi ll 

Native Habitat Preservation Authority 2007).”

Some walnut woodlands in the far eastern end 

of the Puente Hills within the study area were 

impacted by the 2008 Freeway Complex fi re. In 

total, this fi re burned 30,305 acres including 90% 

of Chino Hills State Park. Most of the burned area 

was outside of the study area. The calculated 

acreage burned would make the fi re the fourth 

largest fi re on record in Orange County. Despite 

the fi re damage, a 2010 fi eld visit with California 

State Parks staff to Chino Hills State Park indicated 

that walnut woodlands and forests were making a 

strong recovery from the fi re. Therefore, it is likely 

that the walnut woodlands in the eastern portion 

of the study area will also recover. California State 

Park offi cials stated that wildlife survival was aided 

by the contiguous open space which provided 

suffi cient habitat during fi re recovery. Potential 

threats continued to further recovery include fi re 

and the spread of non-native species.

Criterion 4 Conclusion

The Puente-Chino Hills contain large areas of native 

habitat and a high level of biodiversity despite the 

development that has occurred in the surrounding 

valleys and coastal plain. The Puente-Chino Hills 

meet criterion 4.

Overall Conclusions

The Puente-Chino Hills meet all four criteria for 

national signifi cance:

• The Puente-Chino hills contain a high level 

of biodiversity and outstanding examples of 

southern California communities including 

coastal sage scrub, one of the most 

endangered plant communities in California, 

and the best remaining stands of California 

walnut-dominated forests and woodlands in 

their southern limit of distribution. 

• The Puente-Chino Hills possess exceptional 

quality in illustrating and interpreting natural 

themes of our nation’s heritage, including: 

chaparral, and dry coniferous forest.

• The Puente-Chino Hills feature public open 

spaces and miles of trails that provide 

opportunities such as hiking, biking, horseback 

riding, outdoor education and birding. Excellent 

opportunities are available for scientifi c 

research of native habitats and wildlife.

• The Puente-Chino Hills contain large areas of 

native habitat and a high level of biodiversity 

despite the development that has occurred in 

the surrounding valleys and coastal plain.

Other Signifi cant Resources 

within the Study Area

Portions of the study area that were not included 

in the nationally signifi cant regions are highly 

urbanized. There are nationally signifi cant resources 

in these areas, many of which are fragmented, and 

therefore lack overall integrity. 

Signifi cant Natural Resources

Isolated pockets of rare native plant communities 

can be found in the San Gabriel Valley and Los 

Angeles Coastal Plain. 

Coastal Sage Scrub. The San Jose Hills, located 

just north of the Puente-Chino Hills contain 

excellent examples of coastal sage scrub. These 
 Chapter 3: Resource Signifi cance Other Signifi cant Resources within the Study Area 117

areas have been designated critical habitat for 

the coastal California gnatcatcher. Another 

isolated patch of coastal sage scrub that contains 

designated critical habitat for the coastal California 

gnatcatcher is located in the Montebello hills. 

Although these areas are small and isolated, they 

provide some of the few remaining habitats for the 

gnatcatcher in the Los Angeles basin (USFWS 2007).

Walnut Woodlands and Forest. Walnut 

woodlands in the San Jose Hills are some of 

the best remaining stands of California walnutdominated forests and woodlands south of Ventura 

County (Quinn 1990). 

Riparian Areas. Despite losses of habitat in the 

Los Angeles basin, remaining riparian areas support 

wildlife, primarily migratory and resident bird 

species. This includes federally listed endangered 

species such as the Least Bell’s vireo. Many of these 

remaining areas lie along the San Gabriel River 

in areas such as the Santa Fe Dam and Whittier 

Narrows Recreation Areas. Much smaller fragments 

are located on other portions of the San Gabriel 

River and along a few areas of the San Gabriel 

River’s tributaries such as Walnut Creek, San Dimas 

Wash, and San Jose Creek. 

The Whittier Narrows Dam County Recreation 

Area riparian habitat supports over 300 migratory 

and resident bird species. This area, along with 

several other Los Angeles County Flood Control 

basins, are recognized as “Important Bird Area 

(IBA)” by Birdlife International. IBAs are key sites 

for conservation that: 1) hold signifi cant numbers 

of one or more globally threatened species; 2) 

are one of a set of sites that together hold a suite 

of restricted-range species or biome-restricted 

species; and 3) have exceptionally large numbers of 

migratory or congregatory species.

Also recognized as an International Bird Area 

is the Santa Clara River which supports a high 

number of bird species associated with riparian 

habitat (Los Angeles County Department of Public 

Works 2006a; Audubon Society 2007; San Gabriel 

and Lower Los Angeles Rivers and Mountains 

Conservancy 2001). 

Natural History Themes. Pockets of native 

habitat within the San Gabriel Valley possess 

exceptional quality in illustrating and interpreting 

natural themes of our nation’s heritage, including: 

chaparral, dry coniferous forest, and streams.

Opportunities for Public Enjoyment or for 

Scientifi c Study. Isolated portions of the study 

area offer superlative opportunities for public 

enjoyment. Parks and recreation areas within the 

San Jose Hills and along the San Gabriel River 

feature public open spaces and miles of trails 

that provide opportunities such as hiking, biking, 

outdoor education, and birding. 

High degree of Integrity. This portion of the 

study area lacks a high degree of integrity due 

to urbanization and fragmentation of resources. 

Although areas within the San Gabriel Valley and 

Los Angeles Coastal Plain provide pockets of intact, 

rare native plant communities, the integrity of these 

areas have been highly altered by fl ood control 

projects and subsequent urbanization.

Signifi cant Cultural Resources

Historic Trails and Migration Routes. The 

San Gabriel Valley and the Los Angeles Coastal 

Plain contain cultural resources representing the 

theme “Peopling Places.” These resources, in the 

form of historic trails, played an important role in 

the region’s settlement. Many colonists, traders, 

explorers, and people searching for a better way 

of life dramatically increased the population and 

diversity of the study area. Below is a description of 

these nationally signifi cant resources. 

Juan Bautista de Anza National Historic Trail.

The study area includes 19 miles of the 1,200 mile 

long Juan Bautista de Anza National Historic Trail. 

The trail, designated in 1990, represents the route 

taken by Juan Bautista de Anza in 1775–1776 when 

he led a group of colonists from Mexico into the 

northwestern frontier of New Spain. 

Old Spanish National Historic Trail. The study 

area includes 21 miles of the 3,500 mile long Old 

Spanish National Historic Trail designated in 2002. 

The trail linked Mexican settlements in southern 

California with those in northern New Mexico. 

Route 66. The study area includes 18 miles of the 

2,400 mile long U.S. Highway 66, widely known as 

“Route 66.” Route 66 is signifi cant as the nation’s 

fi rst all-weather highway linking Chicago and Los 

Angeles. 

Portola Expedition. The 1769 expedition of 

Gaspar de Portola and Padre Junipero Serra from 

San Diego to Monterey led to the founding of fi ve 

missions and two presidios in California. From the 

Santa Ana River, the expedition traveled through 

La Brea Canyon, crossed the San Gabriel valley, 

and came to the bank of the Los Angeles River. A 

Portola marker in Brea Canyon marks the site where 

the Portola expedition group camped.

Other Cultural Resources. The Upton Sinclair 

House, a privately owned national historic 
118 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment 

landmark, is located in the city of Monrovia. Upton 

Sinclair was one of the most infl uential American 

novelists focused on social justice in the early 

twentieth century. The house was designated a 

national historic landmark in 1971.

Cultural Themes. There are a few isolated 

areas within the San Gabriel Valley that possess 

exceptional quality in illustrating or interpreting 

resources that represent cultural themes, including 

“Peopling Places,” “Expressing Cultural Values,” 

Developing the American Economy,” and 

“Changing Role of the United States in the World 

Community.” 

Opportunities for Public Enjoyment or for 

Scientifi c Study. Although many historic resources 

lack opportunities to experience historic settings, 

there are many opportunities for interpretation and 

education. Some areas are privately owned and lack 

opportunities for public enjoyment. 

High degree of Integrity. Because of the impacts 

on historic settings, overall this portion of the 

study area lacks unspoiled examples of signifi cant 

resources.

Potential Cultural Signifi cance. Resources 

that are part of the comprehensive fl ood control 

system in the Los Angeles region are located along 

the lower portions of the San Gabriel River. The 

potential signifi cance of that system is described 

under the signifi cance evaluation of the San Gabriel 

Mountains.

OVERALL CONCLUSIONS

Signifi cant resources within isolated areas of this 

portion of the study area meet only three of the 

four criteria for national signifi cance. Exte nsive 

urbanization has fragmented and impacted the 

integrity of the resources in these areas.

Other Recognized Resources

In addition to these nationally recognized cultural 

resources, there are many state and locally 

designated historic resources. These resources are 

described by their associated cultural theme in 

Chapter 2, Resource Description. Other important 

natural resource areas that are not nationally 

signifi cant are also described in Chapter 2.

Photos (from left to right): 1. Jeffrey Pine, San Gabriel Mountains. 2. Lodgepole pine, West Baldy, San Gabriel Mountains. 

Photographs courtesy of Ryan Gilmore. 
 Chapter 3: Resource Signifi cance Other Recognized Resources 119

Table 6: Summary of National Signifi cance

Area / 

National 

Signifi cance

Is it an outstanding 

example of a particular 

type of resource?

Does it possess 

exceptional value or 

quality in illustrating or 

interpreting the natural 

or cultural themes of our 

nation’s heritage?

Does it offer 

superlative 

opportunities for 

public enjoyment, or 

for scientifi c study?

Does it retain a high 

degree of integrity as 

a true, accurate, and 

relatively unspoiled 

example of a resource?

San Gabriel 

Mountains 

YES

Yes, the San Gabriel 

Mountains provide 

outstanding examples 

of geologic resources, 

mountain building, native 

plant communities, 

wildlife, river systems and 

cultural resources related 

to scientifi c research and 

discovery. 

Yes, the San Gabriel 

Mountains possess 

exceptional quality in 

illustrating or interpreting 

natural and cultural themes 

of our nation’s heritage, 

including: mountain 

systems, sculpture of the 

land, river systems and 

lakes, chaparral and dry 

coniferous forest, streams, 

expanding science and 

technology, and expressing 

cultural values.

Yes, the San Gabriel 

Mountains offer 

superlative opportunities 

for public enjoyment and 

scientifi c study. Over 15 

million people live within 

a 90-minute drive to the 

San Gabriel Mountains. 

The mountains have a 

long history of research in 

geology, Mediterranean 

ecosystems, and 

astronomy.

Yes, the San Gabriel 

Mountains retain a high 

degree of integrity and 

are relatively unspoiled 

examples of their type of 

resource, despite impacts 

in some areas from dams 

and reservoirs, utility 

corridors, roads and 

recreational use.

Puente –

Chino Hills

YES

Yes, The Puente-Chino 

hills contain a high 

level of biodiversity and 

outstanding examples 

of southern California 

communities including 

coastal sage scrub, one of 

the most endangered plant 

communities in California, 

and the best remaining 

stands of California walnutdominated forests and 

woodlands in their southern 

limit of distribution. 

Yes, the Puente Chino 

Hills possess exceptional 

quality in illustrating or 

interpreting natural themes 

of our nation’s heritage, 

including: chaparral and dry 

coniferous forest.

Yes, the Puente-Chino 

Hills feature public open 

spaces and miles of trails 

that provide opportunities 

such as hiking, biking, 

horseback riding, outdoor 

education, and birding.

Excellent opportunities 

for scientifi c research 

of native habitats and 

wildlife are available.

Yes, the Puente-Chino 

Hills contain large areas 

of native habitat and a 

high level of biodiversity 

despite the development 

that has occurred in the 

surrounding valleys and 

coastal plain.

Other 

Portions of 

the Study 

NO

Yes, areas within the San 

Jose and Montebello 

hills contain outstanding 

examples of coastal sage 

scrub and California walnutdominated forests. 

Although reduced from 

historic accounts, the 

San Gabriel River and its 

tributaries contain important 

remnant riparian areas that 

provide essential habitat for 

migratory and resident bird 

species.

Outstanding examples of 

cultural resources in these 

historic trails, migration 

routes, and literature.

Yes, isolated native habitat 

within the San Gabriel 

Valley possess exceptional 

quality in illustrating and 

interpreting natural themes 

of our nation’s heritage, 

including: chaparral, dry 

coniferous forest and 

riparian areas.

Cultural resources in other 

portions of the study area 

possess exceptional quality 

in illustrating or interpreting 

resources that represent 

several cultural themes, 

including “Peopling Places,” 

“Expressing Cultural 

Values,” Developing the 

American Economy,” and 

“Changing Role of the 

United States in the World 

Community.”

Yes, isolated areas 

within this portion of 

the study area offers 

superlative opportunities 

for public enjoyment and 

scientifi c study. Parks and 

recreation areas within 

the San Jose Hills and 

along the San Gabriel 

River feature public open 

spaces and miles of trails 

that provide opportunities 

such as hiking, biking, 

outdoor education and 

birding. 

Although many 

historic resources 

lack opportunities to 

experience historic 

settings, there are 

many opportunities 

for interpretation and 

education provided. Some 

areas are privately owned 

and lack opportunities for 

public enjoyment. 

No, this portion of the 

study area lacks a high 

degree of integrity 

due to urbanization 

and fragmentation of 

resources. Although areas 

within the San Gabriel 

Valley and Los Angeles 

Coastal Plain provide 

pockets of intact, rare 

native plant communities, 

the integrity of these 

areas have been highly 

altered by fl ood control 

projects and urbanization.

Because of the impacts 

on historic settings, 

overall this portion of the 

study area lacks unspoiled 

examples of signifi cant 

resources.
120 Draft San Gabriel Watershed and Mountains Special Resource Study & Environmental Assessment