That is a great question that highlights the gap between having the military power to take land and having the strategic reason to keep it. Here is a summary of why Russia ultimately passed on California:
1. The Logistics of Distance
While Spain and Mexico were weak, Russia’s power base was simply too far away. In the early 19th century, communicating with or reinforcing a colony in California from St. Petersburg required a grueling year-long overland journey across Siberia or a massive voyage around the tip of South America. Without a reliable supply chain, California would have been an isolated "island" for Russia.
2. Geopolitical Priorities
The Tsars were far more concerned with European and Ottoman affairs than Pacific expansion. Taking California would have likely triggered a conflict with:
Great Britain: The Royal Navy dominated the seas and would not have tolerated a Russian stronghold on the Pacific coast.
The United States: The rising "Monroe Doctrine" signaled that the U.S. was becoming protective of the Americas. Russia valued the U.S. as a diplomatic ally against Britain and didn't want to jeopardize that relationship for a distant colony.
3. The "Fort Ross" Experiment
Russia actually did have a foothold at Fort Ross (just north of San Francisco) from 1812 to 1841. It was intended to be a "breadbasket" for their starving Alaskan colonies, but it failed to be profitable. The soil wasn't as productive as they hoped, and the costs of maintaining it outweighed the benefits.
4. Overextension
Ultimately, Russia was a continental power. They preferred to expand into neighboring territories like the Caucasus, Central Asia, and the Amur region where they could move troops and resources by land.
Think of it this way: If you were the Tsar, would you risk a global war with the British Navy to defend a piece of land that was currently losing money and was 10,000 miles away?
The "opportunity cost" was simply too high. Russia didn't lose California; they made a calculated decision that it wasn't worth the trouble of holding.