Is it true that in San Francisco during the height of the California gold rush it was more cost effective to ship dirty laundry to China rather than to have it done locally?

Take your pick of China, Hong Kong or Honolulu.

During the 1850's, men outnumbered women in California by 10 or more to one. Women were, therefore, highly valued, both for their company and for the cooking, cleaning and laundry services they performed (laundry cost SO much in California that some men sent their shirts all the way to China to be washed!). Elizabeth Farnham organized the first of several plans for importing women to California.

Lu points out that the origin of Chinese laundry businesses may have begun during the Gold Rush period. "A lot of the miners were men not used to doing women's work," he said. "So they would send their shirts all the way back to Hong Kong to be laundered. That`s when a Chinese enterpreneur thought of the idea of starting a laundry."

http://journalism.berkeley.edu/projects/oakland/culture/ninagr.html

During the California gold rush of 1849, miners sent their laundry to Honolulu for washing and pressing. Due to the extremely high costs in California during these boom years, it was deemed more feasible to send their shirts to Hawaii for servicing.

http://www.sanjeev.net/trivia/during-the-california-gold-rush-of-1849-miners-sent-their-la.html