The Collaborative International Dictionary of English v.0.48:

Placer \Pla"cer\, n.
   One who places or sets. --Spenser.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Placer \Plac"er\, n. [Sp.]
   A deposit of earth, sand, or gravel, containing valuable
   mineral in particles, especially by the side of a river, or
   in the bed of a mountain torrent. [U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

placer
    n 1: an alluvial deposit that contains particles of some
         valuable mineral

U.S. Gazetteer Counties (2000):

Placer -- U.S. County in California
   Population (2000):    248399
   Housing Units (2000): 107302
   Land area (2000):     1404.367303 sq. miles (3637.294463 sq. km)
   Water area (2000):    98.410589 sq. miles (254.882245 sq. km)
   Total area (2000):    1502.777892 sq. miles (3892.176708 sq. km)
   Located within:       California (CA), FIPS 06
   Location:             38.971576 N, 120.947618 W
   Headwords:
    Placer
    Placer, CA
    Placer County
    Placer County, CA