[WildHighlander57]

There’s still a section of I-99 between Sacramento and Bakersfield.

I-5 was built to the west, as a faster route; 99 went through all the towns in the valley.

[Publius]

It's CA 99, not I-99. There are places where I-5 was built separately from the old US 99, and you mentioned one of them.

In California, Oregon and Washington, there are stretches of CA 99, OR 99 and WA 99 that still maintain the original route of the old US 99. In northern Oregon where the old US 99 split into US 99E and US 99W, Oregon maintains the split as OR 99E and OR 99W.