A first thought would be via telegram, but although a telegraph line was established in the United States as early 1844, no telegraph to California was available in 1850: that would come a few years later. However, a person could use the U.S. postal service to mail a letter, since the post office started service to California in November, 1848. By late December, 1848, steamships were carrying letters to California from New York. The steamships would travel from New York to Panama, then, as the Panama Canal was not yet dug, canoes or pack animals carried the mail to the Pacific Ocean (about 50 miles away), where the letters would be loaded on to a waiting ship and carried up to California. As you might imagine, this process was not speedy, especially if you first had to get your letter to New York: there was no overnight communication across America in the year 1850.