Gaviota Soils

On a Wildling Museum outing on Saturday from 9:00 am to 11:30 am, in the series “Natural History Field Classes with Fred and Larry”, a short walk was taken on a trail on the west side of 101 just before it passes through the Gaviota Tunnel. As with most field trips, if I take away about 20% of what is discussed, then my knowledge and understanding has increased by a fragment, upon which I can slowly build more knowledge. Thus, although more than two geologic formations were discussed, two are remembered the most. The next time I go out to that area, I will ignore these two and move onto the next formations that were detailed in a handout.

The two geologic formations that made an impression were Monterey Shale and Rincon Shale. Monterey Shale is found from Northern California to Los Angeles, offshore and to the channel islands. The decomposed organic matter in this shale is the major source of oil extracted in California, and “contains two-thirds of the U.S.’s shale oil reserves”. (Click on any of the images below to see a larger version.)

Monterey Shale

From Wikipedia, “The Rincon Formation (or Rincon Shale) is a sedimentary geologic unit, abundant in the coastal portions of southern Santa Barbara County, California eastward into Ventura County. Consisting of massive to poorly bedded shale, mudstone, and siltstone, it weathers readily to a rounded hilly topography with clayey, loamy soils in which landslides and slumps are frequent. It is recognizable on the south slopes of the Santa Ynez Mountains as the band at the base of the mountains which supports grasses rather than chaparral. The geologic unit is notorious as a source of radon gas related to its high uranium content, released by radioactive decay.”

Giant Rye Grass, Rincon Shale

There were other formations clearly visible from the trail, and this area is apparently one of the few places that many formations can be seen. The Rincon shale, “which supports grasses rather than chapparal” is immediately obvious by looking up the mountain slope on the west. Mustard also grows on Rincon shale, displacing some of the grasses. After a recent fire, when the vegetation was burned, a native fire-follower Giant Wild Rye/Giant Rye Grass started growing in the Rincon shale, and has to some extent replaced or “succeeded” the mustard and/or non-native grasses. (A neat development, because frequently after fires, weedy plants take over.  The “so pretty” mustard is a non-native invasive species.)

Monterey and Rincon Shales

The cliffs of More Mesa, Goleta Slough and other places are also made of Monterey Shale. The cutting at the first part of the Gaviota trail is composed of Monterey Shale, and plants seen on More Mesa cliffs were seen here, too – Cliff Aster and Cliff Buckwheat. Although it is very late in the season, and the last rain fell some six months ago, there were late summer and fall plants blooming. Other Coastal Sage Scrub plants seen around the parking area near the coast and the first part of the trail, were Coastal Goldenrod, California Croton, California Fuschia and Lemonadeberry (the latter seemed to have pre-flowering buds).

Gaviota Tunnel is normally a very windy area, as any movement of the air in the area causes it to rush through the only nearby break in the mountain range. Here many wind-pollinated plants were found. Coyote Brush is found in Coastal Sage Scrub (such as More Mesa and coastal Gaviota). Mulefat, normally found in areas with moister soil, was found as we walked further down the trail to where the clayey Rincon soils abutted the trail. Both of these plants (Coyote Brush and Mulefat) have female and male plants, where the male flowers produce pollen and the female flowers receive the pollen via wind and produce the fruit. In this windy area, the windy airmail delivery system happens more often at the time these flowers bloom – fall. [PLEASE see notes on wind and insect pollination at end of post.]

Further along the trail away from the coast, the normal California Buckwheat, abundant in the Figueroa Mountain area, was found. The leaf difference between the two is that Cliff Buckwheat has triangular-shaped leaves and a white underside. The Chaparral Buckwheat has more spiky, solid green leaves. Both Cliff and California Buckwheat are excellent nectar plants, and a wide variety of butterflies frequent these plants late spring and summer when they bloom.

A single Sacred Datura, highly noxious, was growing low in the grassland. It also grows on More Mesa cliffs, and grasslands elsewhere.

I recorded the sound of a Blue-gray Gnatcatcher, which seems to prefer Coyote Bush in the fall, but the sound of the traffic along 101 drowned out the bird call. Bushtits were seen in a large flock, harvesting the seeds from fennel. And there were a good number of Scrub Jays. A perfect photo of a Bewick’s Wren could have been had, had I had my camera ready. The Wren flew to a bush in front of my car, as I sat inside. Other birds included the Wrentit, the typical Chaparral bird sound, Turkey Vulture and Red-tailed Hawk.

The Gaviota area is also interesting in the spring, with a number of usual and unusual flowering plants. Unfortunately, the area closer to 101 near the turn-off has a ton of non-native invasive plants – and is quite a mess. The stream alongside the 101 apparently was always there, and as the mountains uplifted, it eroded the stream bed downwards to where it remains at sea level.


In the Google map segment above, the green balloons represent photos of plants along the field trip (note the leftmost balloon is a zoom photo from the trail). This satellite image may have been taken in spring when the yellow mustard was blooming – and those areas represent where the Rincon Shale is found. The green area along the west side of 101 is the riparian corridor. The hillsides facing the sea, also face the sun all day, and hence are more barren because they dry out faster. As the top is crested, the slopes going down the other side,  face north and hence are more shaded and greener.


Removed for now.

Dictionary definition and meaning for word carrizo
(noun) tall North American reed having relative wide leaves and large plumelike panicles; widely distributed in moist areas; used for mats, screens and arrow shafts.

Notes on pollination of Baccharis and Artemesia species.
1. Artemesia
“Artemisia L. is a one of main genus of the tribe Anthemideae and also one of the largest genera of the family Asteraceae. It is an eminent wind pollinated cosmopolitan genus, chiefly found in temperate regions of mid to high latitudes of the northern hemisphere, settled in arid and semiarid climates areas and has only a small numbers representation in southern hemisphere (McArthur & Plummer, 1978; Valles & McArthur,  2001).”

2. Baccharis
Whether wind pollinated or insect pollinated or both, is under review, as there have been too many conflicting opinions. However, there is no dispute about wind dispersal of seeds.

Both of the plants mentioned in the post – Mulefat and Coyote Bush are Baccharis species – Baccharis salicifolia and Baccharis pilularis. Quote from “Flora of the Santa Ana River and Environs”: “Baccharis represents the only commonly encountered sunflowers in North America that have separate male and female plants (dioecious)”.