Complex sentence: A Spanish settlement known as Concepción de la Vega gradually grew up around the fort, and after 1508, when gold was found in quantity there, Concepción became the first gold boomtown in the continent.
Split into simpler sentences: A Spanish settlement known as Concepción de la Vega gradually grew up around the fort. After 1508, when gold was found in quantity there, Concepción became the first gold boomtown in the continent.