July 1998

Topanga Watershed covers approximately 12,748 acres (18 square miles).

11,082 acres are undeveloped or held by state and federal park agencies as part of the Santa Monica Mountains National Recreation Area.

There are 4,500 homes in the developed area, with 2 commercial areas, Most of the houses were built between 1950 and 1985. They all have individual septic systems. Only half of all privately owned land in the watershed has been developed. (Info courtesy of Coast and Canyon Realty and NPS)

Years homes built:
before 1949 = 955
1950 -1970 = 1380
1971 -1985 = 1485
1986 -1990 = 499

5 street lights 1 traffic signal
1 turtle crossing sign (3 more coming!)

1960 - under 3,000 1980 - 6,000 1995 - 12,000

4 pre-schools, 2 elementary schools and at least 4 home schools serve almost 1,000 children under 10 years of age.

Topanga Creek is classified as an interrupted stream. It is the third largest watershed draining into Santa Monica Bay.

Major Geologic Formations:
Martinez Formation -50-65 mya
Sespe Formation - 24-36 mya
Topanga and Calabasas Formations - 11-24 mya
Conejo Volcanics

Streamflows (Data courtesy of LA County DPW):
50 year peak flows at Topanga Beach = 21,000 cfs

Rainfall (courtesy of Topanga Volunteers):
22 inches per year average
58.23 inches recorded Jul 1997 - Jul 1998

Biological Resources:

Biodiversity in Topanga is quite high with many species common here that are uncommon in other areas of the Santa Monica Mountains.

Vegetation coverage (courtesy of NPS) according to a modified Holland classification system includes:

Acres Plant Community
900 Coast Live Oak Woodland
318 Riparian Woodland
10 Walnut Woodland
1700 Coastal Sage Scrub
7600 Northern Mixed Chaparral
300 Chamise Chaparral
169 Non-native Grassland
43 Rock Outcrops
20 Coastal Strand (sand)
8 water

Sensitive Plant Species found in Topanga thusfar include:

Astragalus brawntonii -- Braunton's milkvetch
Dudleya cymosa ssp. ovatifolia -- Santa Monica Mountains Dudleya
Hemizonia minthornii -- Santa Susana Tarplant

Critter Count:

Insects -- over 600 species reported
Arthropods -- 50 species
Fish -- 3 species (Steelhead Trout last documented in 1980)
Amphibians -- 7 species (historic location for Red Legged frog)
Reptiles -- 15 species (
Birds -- over 111 noted, 35 confirmed breeders
Mammals -- over 50 species

Sensitive Animal Species found thusfar include:

Oncorhynchus mykiss -- Steelhead Trout
Taricha torosa -- CA Newt
Aneides lugubris -- Arboreal Salamander
Rana aurora draytonii -- CA Red-legged Frog
Clemmys marmorata pallida -- Southwestern Pond Turtle
Phrynosoma coronatum blainvillei -- San Diego Horned Lizard
Cnemidophorus tigris multiscutatus -- Coastal Whiptail
Lampropeltis zonata pulchra -- San Diego Mountain Kingsnake
Masticophis flagellum piceus -- Red Coachwhip
Salvadora hexalepis virgultea -- Coast Patchnose Snake
Thamnophis hammondi hammondi -- Two-striped Garter Snake
Buteo swainsoni -- Swainson's Hawk
Circus cyaneus -- Northern Harrier
Accipiter striatus -- Sharp-shinned Hawk
Accipiter cooperii -- Cooper's Hawk
Elanus caeruleus -- Black Shouldered Kite
Buteo lineatus -- Red shouldered Hawk
Empidonax traillii -- Willow Flycatcher
Lanis ludovicianus -- Loggerhead Shrike
Dendroica petechia -- Yellow Warbler
Icteria virens -- Yellow breasted Chat
Antrozous pallidus -- Pallid Bat
Eumops perotis -- Western Mastiff Bat
Bassariscus astutus -- Ringtail cat
Felis concolor -- Mountain Lion
Felis rufus -- Bobcat

[TCWC Home] [Topanga Online Home]
©1996-98 Sweet Pea Communications. Contents may not be reproduced without permission.
Web page design by Gary Meyer at Sweet Pea Communications