The discovery of blank led to a large population growth in california in the mid 1800s

 GOLD

James Marshall's discovery of gold at Sutter's Mill in California in 1848 led to a "gold rush" in the decade that followed, with 1849 seeing a huge influx of people to California.  (Thus we refer to the '49ers.)  The swift settlement of California added incentive to build a transcontinental railway.  The Pacific Railroad Act of 1862 established the charter for doing that.  The First Transcontinental Railroad was completed in 1869, thus making travel and settlement into California even more accessible.

The discovery of  gold   led to a large population growth in California in the mid 1800s

Explanation:

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the most famous of all the units fighting in cuba, the "rough riders" was the name given to the first u.s. volunteer cavalry under the leadership of theodore roosevelt. roosevelt resigned his position as assistant secretary of the navy in may 1898 to join the volunteer cavalry. the original plan for this unit called for filling it with men from the indian territory, new mexico, arizona, and oklahoma. however, once roosevelt joined the group, it quickly became the place for a mix of troops ranging from ivy league athletes to glee-club singers to texas rangers and indians.