Santiago Peak Volcanic

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Santiago Peak Volcanic Rock On Owen's Peak
© W.P. Armstrong, 8 November 2007
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View of Owen's Peak looking north from the Palomar College Arboretum.

View from Owen's Peak looking southwest toward Palomar College. In the foreground is an outcrop of Santiago Peak Volcanic rock. In the distance is the new Natural Science Building and the Palomar College Arboretum.

An outcrop of Santiago Peak Volcanic rock at the summit of Owen's Peak, better known as Palomar "P" Mountain. This dark, fine-grained, very hard rock dates back to the Jurassic Period, 145 million years ago, to a time when dinosaurs walked the earth. This heavy rock is resistant to erosion and forms some of the higher topography in coastal San Diego County.

An outcrop of Santiago Peak Volcanic rock at the summit of Owen's Peak.

Santiago Peak Volcanic rock from the summit of Owen's Peak.

  Santiago Peak Volcanic Rock In San Dieguito River  
San Marcos Gabbro In Nearby The San Marcos Mts.

An outcrop of Santiago Peak Volcanic rock at the summit of Owen's Peak, better known as Palomar "P" Mountain. This dark, fine-grained rock with white flecks dates back to the Jurassic Period, 145 million years ago. The lemon-yellow, crustose lichen is Acarospora socialis with a small patch of A. bullata (far right). The Acarospora doesn't have the marginally lobate thallus of Pleopsidium flavum and P. chlorophanum. The brown crostose lichen A. bullata is similar to the common species A. fuscata.

  List Of Lichen Images On Wayne's Word  

An outcrop of smooth, white-flecked Santiago Peak Volcanic rock at the summit of Owen's Peak. The foliose lichen is Xanthoparmelia cumberlandia.

The weathered surface of this Santiago Peak Volcanic rock outcrop at the summit of Owen's Peak is covered by colonies of crustose lichen. The circular gray colonies are Dimelaena radiata.

I originally identified this yellow crustose, areolate lichen as Acarospora schleicheri because it lacked the bright chartreuse coloration and marginal lobation of Pleopsidium flavum and P. chlorophanum. However, most modern lichen floras state that A. schleicheri is a soil (terricolous) species. In fact, even A. H. Magnusson (1929) describes A. schleicheri as a soil lichen in "The Yellow Species of Acarospora in North America" (Mycologia 21 (5): 249-260). In the latter reference under "growing on stone" this yellow lichen keys out to A. socialis. According to Kerry Knudson (personal communication, 2007), A. socialis is indeed the correct name for this species. The brown crustose lichen was identified by Charis Bratt as A. bullata. The white crustose lichen with marginal lobation is Dimelaena radiata.

Yellow coblestone lichen (Acarospora socialis) on Owen's Peak. The areoles are about 1-1.5 mm in diameter, some of which contain a sunken hymenial layer. Photographed with Nikon D-40x with manual 55 mm micro-Nikkor macro lens and 3 extension rings at f-22 (one second exposure).

Magnified view of yellow coblestone lichen (Acarospora socialis) and tardigrade (black arrow) on Owen's Peak. The areoles are about 1-1.5 mm in diameter, some of which contain a sunken hymenial layer. The tardigrade is only about 0.25 mm long (1/100 of an inch).

Minute tardigrades (Phylum Tardigrada) are only about 0.25 mm long (1/100 of an inch). Although they are fairly common on mosses and lichens, they are rarely seen. They are called "water bears" because of their fat body with stubby legs bearing claws at the tips.