D. California and New Mexico became new states is not a provision of the Compromise of 1850.
A provision of the Compromise of 1850 was the establishment of the territories of New Mexico and Utah, where the settlers would decide whether to allow or prohibit slavery. Additionally, the slave trade was abolished in Washington D.C., but slavery was still legal there. The compromise also included a more stringent Fugitive Slave Law that required citizens to aid in the capture and return of runaway slaves to their owners, even if they were in free states.
Therefore, the correct answer is: C. Native Americans living in New Mexico would decide whether the territory joined the United States.