A gold rush always brings new arrivals from many directions. Had any of the miners and businesspeople of the 1849 California Gold Rush come from Russia?
Yes, there were. The Russian-American Company sent a party of prospectors comprised of four Russians and six Tlingit indians led by a Lt P.P. Doroshin:
Doroshin and 10 RAC employees sailed to California aboard the Prince Menshikov, which arrived in the overnight boom town of San Francisco on December 21, 1848. In January, 1849, Doroshin set out with his crew of six European prospectors and four Tlingits up the Sacramento River basin to gold diggings along the Yuba River.
Details with dates and amounts (about 43 pounds of gold) mined can also be found in the book The Tlingit Indians in Russian America, 1741-1867 By A. V. Grinev.
You can also do wildcard searches in the 1850 US census and the 1852 California census and find examples of other individuals with the place of birth listed as Russia.
According to this article on the California Gold Rush:
Fully one-third of the “forty-niners” were immigrants... The immigrant groups were equally diverse, coming from Mexico, China, France, Germany, Russia, Ireland, Italy, the West Indies, and even as far away as Australia.
While I don't have any documentation, my family has a story of my grandfather's great (or great-great) uncle Isaac Sommer who was the first mate/accountant on a Russian trading ship. He was Jewish (which is why he did the "dirty work" of handling the finances). As the story goes, Isaac was on the trading ship as it was coming down the California coast, loaded with furs and other goods. When the ship docked in San Francisco, the crew heard about gold in the hills, and they jumped ship to find their fortune. This left the Isaac and the captain with the ship and no way to get it back. They sold the ship and the goods on it, and set up one of the first pawn shops on the Embarcadero. Bit by bit, Isaac sent for the rest of his family to come to San Francisco, where my grandfather was born in 1903.
I have no way to verify this story, but I would love to be able to.
This is quite likely, since the Russian post of Fort Ross was located just a couple hundred miles north of California. Since Fort Ross specialized in fur trade, a gold rush would have attracted many (relatively poor) Russians from that trading post.
Unfortunately, however, few records were kept of the early days of the California Gold Rush (when most of the Russians would have come to California), so it wouldn't be easy to find physical evidence of the presence off Russians there.