Meaning

noun a leaven of dough in which fermentation is active; used by pioneers for making bread

noun a settler or prospector (especially in western United States or northwest Canada and Alaska)

originFrom Middle English sour dogh, equivalent to sour + dough, compare German Sauerteig and Dutch zuurdeeg. The senses pertaining to California, Alaska and the Yukon derive from the distinctive pouches of bread starter (starter dough used to make sourdough) worn on a belt or around the neck by experienced prospectors during the Klondike Gold Rush and California Gold Rush.

Etymology from Wiktionary, CC BY-SA 3.0