There was a MARITIME FUR RUSH.
The earliest record of fur being traded with Europeans in California was in 1733 of Spanish missionaries trading with tribes in upper and lower California for sea otter pelts.
In 1778 Captain James Cook’s third voyage, otter skins were obtained at Nootka Sound on the Northwest Coast and, although Cook was killed in Hawaii on the way to China, his men were shocked at the high prices paid by the Chinese.[4] A profit of 1,800% was made.
When the accounts were published and EVERYONE wanted to do it. The Boston sailing ships took over the trade and used sales of sea otter from California to pay off debts from the revolutionary war.
They found that beaver skins were equally valuable and started trading with the natives for those too. All before the first mountain man ever crossed the border into the golden state.