relict alluvial and lacustrine surfaces that rarely, if 

 ever, are subject to flooding. Where through-drainage 

 systems are well developed, alluvial plains are domi- 

 nant and lake plains are absent or of limited extent. 

 Basin floors grade mountainward to distal parts of 

 piedmont slopes, (figs. B-3 and B-5) HP 



Basin-floor remnant — A flattish topped, erosional rem- 

 nant of any former landform of a basin floor that has 

 been dissected following the incision of an axial stream. 

 FFP 



Beach — The unconsolidated material that covers a gently 

 sloping zone, typically with a concave profile, extend- 

 ing landward from the low-water line to the place where 

 there is a definite change in material or physiographic 

 form (such as a cliff) or to the line of permanent vege- 

 tation; the relatively thick and temporary accumula- 

 tion of loose water-borne material (usually well-sorted 

 sand and pebbles, accompanied by mud, cobbles, boul- 

 ders, and smoothed rock and shell fragments) that is in 

 active transit along or deposited on, the shore zone 

 between the limits of low water and high water. GG 



Beach plain — (See wave-built terrace.) 



Beach ridge — A low, essentially continuous mound of 

 beach or beach-and-dune material heaped up by the 

 action of waves and currents on the backshore of a 

 beach, beyond the present limit of storm waves or the 

 reach of ordinary tides, and occurring singly or as one 

 of a series of approximately parallel deposits. The 

 ridges are roughly parallel to the shoreline and repre- 

 sent successive positions of an advancing shoreline. GG 



Beach terrace — A landform that consists of a wave-cut 

 scarp and wave-built terrace of well sorted sand and 

 gravel of marine or lacustrine origin. In some places it 

 occurs on a lower piedmont slope. FFP 



Bedrock — The solid rock that underlies the soil and other 

 unconsolidated material or that is exposed at the sur- 

 face. (See regolith.) HP 



Bench — (See structural bench.) HP 



Berm — A low impermanent, nearly horizontal or landward- 

 sloping bench, shelf, ledge, or narrow terrace on the 

 backshore of a beach, formed of material thrown up 

 and deposited by storm waves; it is generally bounded 

 on one side or the other by a beach ridge or beach scarp. 

 Some beaches have no berms, others have one or sev- 

 eral. A synonym for berm is backshore terrace. GG 



Block field — A thin accumulation of usually angular 

 blocks, but subrounded to subangular in some places, 

 with no fine sizes in the upper part, over solid or 

 weathered bedrock, colluvium, or alluvium, without a 

 cliff or ledge above as an apparent source. Blocks are 



often upheaved from intensive frost shattering of jointed 

 bedrock. Block fields occur above tree line and in polar 

 regions on slopes of less than about 9 percent (5°). A 

 synonym for block field is felsenmeer. GG 



Bluff — (a) a high bank or bold headland, with a broad, 

 precipitous, sometimes rounded cliff face overlooking 

 a plain or body of water, especially on the outside of a 

 stream meander; (b) any cliff with a steep broad face. HP 



Bog — Waterlogged, spongy ground, consisting primarily 

 of mosses, containing acidic, decaying vegetation such 

 as sphagnum, sedges and heaths, that develops into 

 peat. (See fen.) GG 



Bolson — An internally drained (closed), intermontane 

 basin with two major landform components: basin 

 floor and piedmont slope. The former includes nearly 

 level alluvial plains and playa-like depressions. The lat- 

 ter comprises slopes of erosional origin adjoining the 

 mountain fronts (pediments) and complex construc- 

 tional surfaces (bajadas) mainly composed of individ- 

 ual and/or coalescent alluvial fans. Bolson is a regional 

 term used in the Southwest, (fig. B-3) HP 



Braided channel or stream (flood plain landforms) — A 

 channel or stream with multiple channels that inter- 

 weave as a result of repeated bifurcation and conver- 

 gence of flow around interchannel bars, resembling in 

 plan the strands of a complex braid. Braiding is gener- 

 ally confined to broad, shallow streams of low sinuos- 

 ity, high bedload noncohesive bank material, and steep 

 gradient. At a given bank-full discharge, braided streams 

 have steeper slopes, and shallower, broader and less 

 stable channel cross sections than meandering streams. 

 (See flood plain landforms.) HP 



Break (slopes) — A marked or abrupt change or inflection 

 in a slope or profile; a knickpoint. GG 



Breaks — The steep to very steep broken land at the border 

 of an upland summit that is dissected by ravines. HP 



Breccia — A coarse-grained, clastic rock composed of 

 angular rock fragments (larger than 2 mm), commonly 

 cemented together in a finer-grained matrix of varying 

 composition and origin. The consolidated equivalent 

 of rubble. (See conglomerate.) HP 



Buried — Pertaining to landforms, geomorphic surfaces, 

 and paleosols covered by a mantle of geologic material 

 (for example, sedimentary or volcanic). HP 



Butte — An isolated, usually flat-topped upland mass 

 characterized by summit widths that are less than heights 

 of bounding erosional scarps. An upland type produced 

 by differential erosion of nearly horizontal, interbed- 

 ded weak and resistant rocks, with the latter compris- 

 ing caprock layers. As summit area increases relative to 



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