Marine Corps Air Station Miramar is host to thousands of fragile vernal pools.
The Marines know that, and are spending millions of dollars
to locate, catalog, protect and restore these pools.
This article covers the area known as Miramar Mounds,
located at the south end of Miramar West.
[Click the map to enlarge it]
This article covers the area known as Miramar Mounds,
located at the south end of Miramar West.
[Click the map to enlarge it]
Miramar Mounds National Natural Landmark
Designated: 1972 — Acres: 389
Ownership of the land: Federal
Miramar Mounds contains unique soil features called "mima mounds,"
Many theories exist as to what created the Mima Mounds;
causes ranging from geologic forces to extraterrestrial beings
have been cited for their origin.
Designated: 1972 — Acres: 389
Ownership of the land: Federal
Miramar Mounds contains unique soil features called "mima mounds,"
Many theories exist as to what created the Mima Mounds;
causes ranging from geologic forces to extraterrestrial beings
have been cited for their origin.
There's really nowhere safe to stop here, so these pictures are taken on the go.
Found on another Mima Site: No one is sure of how the Mima Mounds were formed.
They are dirt piles 3-6 ft. tall, spaced somewhat regularly 20-30 ft. apart.
Three predominant theories exist about their formation:
- Glaciers left sediment as they melted 12,000 years ago; erosion formed the mounds.
- Seismic activity from earthquakes formed the mounds.
- Large numbers of pocket gophers created the mounds.
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Can I help it if the road to the necessary wine shop
goes through vernal pool home territory?
Vernal pools are commonly associated with Mima Mounds in California.
Mima Mounds are located on stable landforms older than 100,000 years.
These landforms tend to be soils that feature impermeable layers
(claypan or silcrete duripan) in the subsoil.
This layer impedes drainage and creates perched water levels.
Vernal pools form between the mounds; they are typically
small, shallow, complex wetlands with only internal drainage
because they are hydrologically isolated from perennial inflow by mounds.
Although water that fills vernal pools comes and goes during a year,
it is present at least for a short time in most years.
In North America, Mima-type earth mounds are found west of the Mississippi River from southern Canada to northern Mexico. They occur on poorly drained soils with a shallow basement layer or permanent water table.
In San Diego County, California, Mima mounds are found at the edge of coastal salt marshes above a shallow water table, on coastal marine terraces having a cemented, clay-capped hardpan, on foothill slopes and stream-cut terraces over shallow bedrock, and in cis-montane valleys, mountain meadows, and the margins of desert-edge marshes where a dense sub-surface clay layer creates poor drainage.
Major hypothesis of mound orgin involve (1) frost-sorting, (2) erosion, (3) wind disposition, and (4) fossorial rodent actitivy.
At Miramar Mounds National Landmark in San Diego, soil samples (1980 cm^3) were collected from the tops, edges, and neighboring basin centers of 10 mounds for analysis of small rock content. Soil plugs with metal markets were inserted in pocket gopher tunnels at mound edges, and the movement of these markers traced with a metal detector. Mounds on a 0.58-ha plot were mapped and their dimensions measured.
Contrary to all but the fossorial rodent hypothesis, gravel and small pebbles that such rodents are able to move were concentrated in mound soils. Clearing of the experimental soil plugs by pocket gophers was accompanied by a significant moundward translocation of mined soil. The spacing of mounds tended towards uniformity, but intermound distance increased with increased significantly with increase in mound size.
The distribution of mound fields in San Diego County corresponds closely to the distribution of original valley grassland inferred for a 10-yr fire cycle. It is hypothesized that Mima mounds are an indicator of original grassland environments.
