You can delay the discovery of gold a little, but delaying it 25 years is going to require people of European ancestry not settle in the area and even that that might not be enough. That probably requires a divergence far enough back that there may not be a USA.
Perhaps in 1542 the Cabrillo expedition to Alta California misses San Diego Bay. (After all, it missed the San Francisco and Monterey Bays.) Spain doesn't find a decent west coast harbor until the 1602 Vizcaino expedition.
Fast-forwarding, if there is a USA, lack of population means California statehood is delayed. Likely that means no Compromise of 1850 - there don't become more free states than slaves states until Minnesota becomes a state in 1858, nor is there a Fugitive Slave Law. The first means southern leadership is less disgruntled since there's a balance of free and slave states in Congress. The second means northern states aren't hoping made about thier states' rights being trampled to preserve slavery.
Tensions still exist as it becomes obvious the Midwest and West will be coming in as free, not slave states. There will probably still be a Bleeding Kansas and a decent chance the Sumner caning still occurs. 1858 probably sees an attempt to maintain the balance of power by admitting Minnesota as a free state and Kansas as a slave state under the Lecompton Constitution.
The question is then if northern Democrats would support the Lecompton Constitution to try to hold their party together, or oppose it as a fraud. If they support it, most of the north and some of the border south will move towards a Republican party. If they oppose it, the Democratic Party probably fractures like in OTL.
Either way, you get a Republican President in 1860. If the Democrats fractured, the southern branch will likely attempt secession and things will probably be similar to OTL. If the Democrats hang together, this first term will likely see at least one of California, Oregon, and Nevada trying to enter as a free state.
And that should have the Fire-Eaters less than pleased. By 1864, slave states are outnumbered in the Senate. I'd expect them to split the Democratic Party, guaranteeing a Republican win. So we get secession attempted 4 years later, with the border south less likely to leave than in OTL. Odds are probably worse for the CSA than in OTL.