Highway 38 is the back way up. Where Highway 18 takes the front face in a hurry, 38 leaves Redlands and draws the long line: up Mill Creek, past the Forest Falls turn, through Angelus Oaks and Barton Flats, along the upper Santa Ana River, then a steady grind to Onyx Summit at 8,443 feet. No state highway in Southern California crosses higher. Onyx Peak stands just above the road at 9,114.
It is worth taking as geography rather than as a shortcut, because it is not one; it is a good deal longer than the direct climb. What it follows is the Santa Ana River nearly to its headwaters, which is the same water Bear Valley Dam was built to hold and the same water Redlands was built on. Drive it uphill and you are running the valley's water supply backwards.
The San Bernardino Mountains lie east to west across a state whose ranges mostly run north to south. They are a transverse range, pushed up along the San Andreas over something like the last eleven million years and still rising, which is why the front face is so abrupt and why this road has to work so hard to get over it.
North of the summit the country changes over. The pines thin, junipers come in, and the descent toward Big Bear and Baldwin Lake opens on the Mojave beyond. The Pacific Crest Trail crosses close by. There is a paved pullout at the top, and a granite crag about a quarter mile north of it that climbers work.
The highway is plowed, but it closes in storms and chain control is common through the winter.
The closest stops worth working into your route
Roadside plaques and monuments within a short detour