The Collaborative International Dictionary of English v.0.48:

Bonanza \Bo*nan"za\, n. [Sp., prop. calm., fair weather,
   prosperity, fr. L. bonus good.]
   In mining, a rich mine or vein of silver or gold; hence,
   anything which is a mine of wealth or yields a large income.
   [Colloq. U. S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

bonanza
    n 1: an especially rich vein of precious ore
    2: a sudden happening that brings good fortune (as a sudden
       opportunity to make money); "the demand for testing has
       created a boom for those unregulated laboratories where boxes
       of specimen jars are processed like an assembly line" [syn:
       boom, bonanza, gold rush, gravy, godsend, manna
       from heaven, windfall, bunce]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "bonanza":
   Eldorado, Golconda, abundance, affluence, ample sufficiency,
   ampleness, amplitude, avalanche, bountifulness, bountiousness,
   bumper crop, copiousness, cornucopia, eldorado, extravagance,
   exuberance, fertility, flood, flow, foison, font, fount, fountain,
   full measure, fullness, generosity, generousness, gold mine,
   gravy train, great abundance, great plenty, gush, house, landslide,
   lavishness, liberality, liberalness, lode, lots, luxuriance,
   maximum, mine, mine of wealth, more than enough, mother lode, much,
   myriad, myriads, numerousness, opulence, opulency, outpouring,
   overflow, plenitude, plenteousness, plentifulness, plenty,
   prevalence, prodigality, productiveness, profuseness, profusion,
   quantities, quarry, repleteness, repletion, resource, rich harvest,
   rich lode, rich uncle, rich vein, richness, riot, riotousness,
   scads, shower, source, source of supply, spate, spring, staple,
   stream, substantiality, substantialness, superabundance,
   teemingness, treasure, treasure trove, treasury, vein, wealth,
   well, wellspring



U.S. Gazetteer Places (2000):

Bonanza, AR -- U.S. town in Arkansas
   Population (2000):    514
   Housing Units (2000): 219
   Land area (2000):     1.227708 sq. miles (3.179750 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    1.227708 sq. miles (3.179750 sq. km)
   FIPS code:            07540
   Located within:       Arkansas (AR), FIPS 05
   Location:             35.237676 N, 94.428892 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Bonanza, AR
    Bonanza


U.S. Gazetteer Places (2000):

Bonanza, CO -- U.S. town in Colorado
   Population (2000):    14
   Housing Units (2000): 33
   Land area (2000):     0.438258 sq. miles (1.135082 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.438258 sq. miles (1.135082 sq. km)
   FIPS code:            07571
   Located within:       Colorado (CO), FIPS 08
   Location:             38.295138 N, 106.140158 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Bonanza, CO
    Bonanza


U.S. Gazetteer Places (2000):

Bonanza, GA -- U.S. Census Designated Place in Georgia
   Population (2000):    2904
   Housing Units (2000): 976
   Land area (2000):     1.214198 sq. miles (3.144758 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    1.214198 sq. miles (3.144758 sq. km)
   FIPS code:            09272
   Located within:       Georgia (GA), FIPS 13
   Location:             33.464663 N, 84.337589 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Bonanza, GA
    Bonanza


U.S. Gazetteer Places (2000):

Bonanza, OR -- U.S. town in Oregon
   Population (2000):    415
   Housing Units (2000): 152
   Land area (2000):     0.833686 sq. miles (2.159238 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.833686 sq. miles (2.159238 sq. km)
   FIPS code:            07300
   Located within:       Oregon (OR), FIPS 41
   Location:             42.199333 N, 121.404639 W
   ZIP Codes (1990):     97623
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Bonanza, OR
    Bonanza