Final answer:
The correct answer is 'D. Opposition to slavery, as this was not a reason used by Southern California to justify separating and forming their territory. Separation movements were primarily driven by economic, cultural, and geographical factors in other parts of California. The correct option is D. Opposition to slavery
Step-by-step explanation:
The reason opposition to slavery is NOT one Southern California used to justify separating from the rest of California and forming their own territory. Economic, cultural, and geographical factors were often key motivators behind such separatist movements.
During the period when California was discussing statehood, the question of whether it would be a slave or free state was indeed contentious.
However, the secessionist movements within California, such as the desire to form the State of Jefferson in northernmost counties, were driven by feelings of political isolation and cultural differences rather than slavery, especially considering that California entered the Union as a free state and did not have the same economic reliance on slavery as the Southern states. The correct option is D. Opposition to slavery