Which is territory became the first state west of the rocky mountains due to its rapid increase in population during the mid 1800s a.)oregon b.)nevada c.)utah d.)california

A.) Oregon is the territory that became the first state west of the Rocky Mountains due to its rapid increase in population during the mid 1800s.

In 1842 up to 1843, many settle in the Oregon country. Those settlers used the Oregon trail. The Oregon territory was officially organized in 1848. Population grew because of the Donation Land Claim Act of 1850 and many displaced natives were forced to settle in the reservations in Oregon. Oregon became a state in 1859.