. Bulletin. Science; Natural history; Natural history. 168 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Fig. 3. Bahia de San Quintin showing the typical littoral zones of the salt marsh. created by offshore mud flats, a particularly peaty substrate that has a high water retaining capacity, or to the subsurfacing of fresh waters draining the adjacent volcanic cone and lava beds. Shoreline marsh physiography.—The fringe marshes are discontinuous and lim- ited to shoreline edges. They tend to be less than 25 m wide and are generally devoid of tidal channels, although they are readily inundated during
. Bulletin. Science; Natural history; Natural history. 168 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Fig. 3. Bahia de San Quintin showing the typical littoral zones of the salt marsh. created by offshore mud flats, a particularly peaty substrate that has a high water retaining capacity, or to the subsurfacing of fresh waters draining the adjacent volcanic cone and lava beds. Shoreline marsh physiography.—The fringe marshes are discontinuous and lim- ited to shoreline edges. They tend to be less than 25 m wide and are generally devoid of tidal channels, although they are readily inundated during high tides. Some of the marshes are level, others grade gently toward the Bay, and still others are somewhat terraced. The mud and silt substrates are shallow and firm, usually less than 25 cm thick, and are often overridden by erosional deposits of sand, loam, volcanic ash, and lava from adjacent uplands. In many places these marshes have become established on inundated upland soils. The bayward edges of these narrow marshy strips are abrupt and consist of water worn clay ledges, exposed sand bars or lava rock rubble, stratified beach rock created by the freshwater deposition and lamination of calcium carbonate in sand and loam, or in a few places, beaches stabilized by accumulations of mollusk shells. Shoreline marshes which are exposed to constant wave action or strong tidal currents along the open water edges and generally lack Spartina. Transition zone physiography.—The most common ecotones between marsh- lands and upland vegetations occur on variable slopes in stabilized sandy loam hills. A few marshes are backed by abrupt aa' lava flows or sand dunes. Recently disturbed dunes have spread directly into the marshlands as a result of strong northwest winds. Most of the transition zones occur on relatively steep slopes, and vegetation changes are abrupt. The transition in Punta Azufre marsh extends onto a salt playa. The slope is nearly level and the transition zone is
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