Why did the possibility of individuals making a fortune in California

Why did the possibility of individuals making a fortune in California through the panning, sluicing, and cradling of gold essentially evaporate by 1851?

A) Gold mining had become transformed into large-scale hydraulic mining, requiring large corporate investments and reducing miners to hired labor.
B) The Gold Rush had exhausted the supply of gold to be mined in California by 1853.
C) Hired laborers could now make a small fortune working for large-scale, hydraulic mining operations.
D) The fierce competition from African slaves and Indian miners overwhelmed the ability of individual miners to make their fortunes.

ANSWER
Answer: A