The president of the united states at the time both oregon and california were officially acquired was

James K. Polk

Explanation:

James Knox Polk became the eleventh president of the United States in 1845 and served till 1849. As he promised during his election campaign he did not contest for the second time. His tenure is important because the territories of the United States increased one third. He secured Oregon territory from the Britishers and California after the American-Mexican war which stretched from 1846 to 1848.