Chapter 11 - ACECs
Coast Management Area

Tierra Redonda

Tierra Redonda Mountain, situated in northwestern San Luis Obispo County between Lake Nacimiento and Lake San Antonio, is located about 20 miles east of the Pacific Ocean and 20 miles northwest of Paso Robles. The Tierra Redonda ACEC encompasses 320 acres of Federal surface and 80 acres of Federal mineral estate.

Tierra Redonda Mountain was designated as open space in the San Luis Obispo County General Plan to retain areas with fragile plant or animal communities in a natural or undisturbed state. The dominant plant community is blue-oak woodland. Grassland, chaparral, and unique sand dunes also occur here. The site is valuable for its biodiversity, scenic views, wildlife habitat, and geology. The area contains several rare or endemic plant species. One of the largest concentrations of Chorizanthe species in the world is found here. Sensitive plant species include one-awned spineflower, Salinas Valley goldfields, San Luis Obispo County lupine, and ribbonwood. San Luis Obispo County lupine is the official flower for the county. Prairie falcons are also known from this area.

Tierra Redonda Mountain is also the type area for the Tierra Redonda Formation, a sequence of marine sedimentary rocks. This is its thickest locality, where it forms sandstone cliffs. On the south side of Tierra Redonda Mountain, the Vaqueros Formation underlies the Tierra Redonda Formation. The Vaqueros Formation is highly fossiliferous. In places the formation contains fossil mollusks, echinoids, sand-filled worm tubes, foraminifers, bone and fish scales.  Mollusk shells and fragments are common. Other beds are composed almost entirely of oyster shell fragments.

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On the south side of Tierra Redonda Mountain are sandy beds several feet thick, composed almost entirely of fossil turritellas. This feature is extremely rare. Further investigation is needed to understand this unique habitat. The sandstone cliffs provide habitat for nesting birds.

This area is considered to have moderate occurrence potential for oil and gas, and moderate occurrence potential for phosphate.

Very little land administered by the Caliente Resource Area within the Coast Ranges is underlain by the Vaqueros or Tierra Redonda Formations. This site provides students and scientists the opportunity for continued study of the geology, stratigraphy and paleontology of these rocks.

No oil and gas leases, mining claims, or land use authorizations occur within this ACEC. South of Tierra Redonda Mountain, most of the adjacent private land has been developed for residences associated with the "community" of Oak Shores.

Because the area has a number of sensitive resources and development is rapidly encroaching, ACEC designation is warranted to protect these resources.

Objective     Manage Tierra Redonda Mountain ACEC to protect the paleontological resources, the unique sand dune formation, coast live oak woodland, scenic view, and the type locality for the Tierra Redonda rock formation.

Management Prescriptions

This ACEC is open to leasing of oil, gas, and geothermal resources subject to NSU.

The ACEC is proposed for withdrawal from entry under the mining law.

The ACEC is unavailable for livestock grazing due to it's unsuitability.

Sand dunes are limited to pedestrian access only.

Legal Description

T. 25 S., R. 9 E., MDB&M
Sec. 10 S½NE¼, NE¼SW¼, N½SE¼
Sec. 11 SW¼NE¼, SE¼NW¼, N½SW¼, NW¼SE¼

Area Map

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