Okay, so assuming Spain follows relatively OTL, the gold will likely not be encountered until the exploratory missions of California in the 1760s and 1770s. Let's say for the sake of simplicity 1778, a soldier posted at one of the missions discovers gold after taking a break near a stream. Unlike OTL's gold rush, there is much less infrastructure in the region to support or communicate the gold rush, and the first to hear about it will be sailors in the Pacific (mostly Spaniards at this point, the maritime fur trade was only beginning) and the folks in New Spain, who will probably leap at the chance for acquiring easy gold. Next to hear are traders in Manila and the Spanish Caribbean, which is where non-Spanish folks begin hopping on the gold rush wagon.
In this scenario the USA exists, but nothing guarantees it will be anything like the state of OTL, given California will probably attract many young men from the Thirteen Colonies looking for some chance to get rich quick who otherwise might've done something to the cause. The Gold Rush if anything might lead to a situation where Spain is more hesitant to provoke Great Britain, given the frailty of it's California colony and treasure ships bringing loot back to Spain. Though, alternatively, Spain had a lot of grievances with Britain that were worthy of going to war over, and with some extra gold in hand, they had a bit more loot to pay for armaments with. Either way, there's no guarantee the US becomes the landgobbler of OTL. It's early enough for the Revolution to fizzle out and die even, though that is less likely should the war go as international as it did OTL.
With regards to Indians, The Spanish were no stranger to cruelty and genocide when natives stood in their way of treasure. Their luck might be slightly better than OTL, as the Missions essentially wanted to function as a place to 'kill the Indian to save the man' and at bare minimum would act as a anti-Indian Extermination bulwark. I can see the Missions essentially becoming functional Indian reserves, with the settlers driving many Native peoples off their land, and the natives out of desperation seeking out missions as sanctuaries from persecution. Not a pleasant fate, but a minor step up from the extermination campaign of OTL.
China is not as deep in the bucket as it was in the 1840s, but certainly there will be immigrants attracted by stories of easy gold. Hawaii is pre-unification, and though it's also not really been woven into the global economy as much as it had been in the 1840s, so there probably aren't any kanakas in the goldfields. Obviously Europe is going to see a number of immigrants flocking to California, though New Spain might try to weed out Protestants from immigrating to California. Obviously people from all across the Spanish Empire will pour in from Manila to Buenos Aires.
As San Francisco booms into a busy port, Spain has much more incentive to port-hop into the Northwest, especially to stave off Russian and British efforts to threaten California. So in addition to Spanish exploration and solidifying control of Louisiana, there will likely be an attempt to make California-style fortified missionary ports further north, probably at OTL Eureka, Astoria, Greys Harbor, and Anacortes. Now assuming the US can get on it's feet, the Maritime fur trade will be much harder to enter, and the China trade, a lucrative part of the early US economy will be a little harder to get into.