Sourdough is most associated with pioneers, but the Alaska Gold Rush made Sourdough bread famous, as it was the most popular and practical food for the pioneers and prospectors.

Prospectors could not rely on buying yeast - it was expensive, difficult to get, and oftentimes dead upon arrival due to the extreme conditions during transport. They learned to create their own yeast naturally using the limited ingredients available - potatoes, flour, water. With these basic items and time, a starter was developed containing wild yeast the winds would carry by.

Sourdough is essentially a living thing containing yeast and friendly bacteria  Lactobacillus creating an environment for leavening. Together they create gas which makes bread rise and gives it a unique and tangy flavor.

Using part of the sourdough starter, flour and other ingredients are added to make bread. The remaining sourdough starter is saved to create more starter, usually by adding more water and flour.  This is what makes sourdough a continuous bread source, and why sourdough was a very important staple in the prospector's diet.