Raisins in California  
Land prices in the 1870's ranged from $3 - $20 per acre in California so large "spreads" could be bought inexpensively. As word of potential profits spread, land in the San Joaquin became a very attractive investment for developers and farmers. 
                                                                                 In the late 1800's many Armenians, recognized as some of the world's most experienced  viticulturists, came to the Central Valley. Even today, many raisin growers in California are of Armenian descent. Later, in the 1950's, immigrant farmers from India found great success in the raisin industry and play a big part in the industry today.        
While the muscat grape was generally regarded as the best raisin producer, it was a seeded raisin and  the consumer didn't like seeds. Consequently, muscat raisins had to be seeded and this meant that the seeds were forced through the skin of the grapes, resulting in a sticky raisin. Raisin sales in the 1870's were limited to people willing to separate the sticky raisins by hand. What the growers needed, to expand consumer interest, was a perfect seedless raisin grape. 
Enter William Thompson and His Grape
In 1876, a Scottish immigrant living in the Northern Sacramento Valley became the man that answered all the raisin growers' prayers. William Thompson first introduced the Lady deCoverly seedless grape - a thin-skinned, seedless, sweet and tasty grape - at the Marysville (California) District Fair. 
These grapes, which would later become known as Thompson Seedless grapes, were precisely what the industry needed. 
And here we are today: Popular as a table grape, Thompson Seedless are still the best grapes for making raisins. Ninety-five percent of the raisins produced in California today are made from Thompson Seedless grapes grown in the San Joaquin Valley.