Road conditions Highway Amy 5 from Oregon to California

So you are thinking 84 to Ontario, 95 into Nevada, and finally 6 into California.

Once you've crossed the Washington Cascades the only mountains are the Oregon Blues, which can be as snowy. Check Oregon Tripcheck for conditions. Once you are past the Ontario/Boise farming area, it's sparsely settled desert like. Jordan Valley is a small settlement with a bit of a Basque heritage.

An alternative would be US97 to Bend, 20 to Burns and OR78 to US95. No mountains this way.