During the california gold rush, about 25,000 laborers migrated to california from

China

Explanation:

Early in 1849 the news of the gold fever was already known all over the world, and a huge amount of gold researchers and dealers began arriving from almost every continent.

Those who came from Asia, especially from China, began to arrive in 1849, initially in small numbers. In Chinese, California was called the "Golden Mountain."

the answer is a, salt plain