Rim of the World Scenic Byway

Cajon Pass to Mill Creek

Southern California · California · United States

Key measurements

Distance

106.1 miles

Elevation gain

11,596 ft

Elevation loss

12,052 ft

High point

8,449 ft

Low point

2,690 ft

Net change

-460 ft (3,150 ft to 2,690 ft)

Surface

Paved

Route type

point-to-point

Route Overview

This 106-mile ride crosses the high crest of the San Bernardino Mountains, transitioning from the dry Mojave Desert fringe at Cajon Pass to the low-elevation citrus belt and chaparral of Mill Creek. Along the way, the route climbs over 11,500 vertical feet, riding long stretches of the Rim of the World Highway (CA-18) and crossing Onyx Summit on CA-38 at 8,448 feet before a dramatic canyon drop back to the Inland Empire floor.

The terrain varies from open desert-foothill sweeps and dense montane pine canopy around Lake Gregory and Lake Arrowhead to wide alpine valley floors around Big Bear Lake and narrow rock wall gorges in Mill Creek Canyon. It is a dense, high-elevation mountain traverse defined by constant cornering, rapid ecological transitions, and broad vistas over the Southern California inland basin.

Key Segments & Geographic Transitions

High Desert Foothills & Silverwood Approach — Miles 0.0–17.1

Starting in the high-desert scrub of Cajon Pass, CA-138 skirts the northern base of the San Bernardino range. The road presents wide-radius curves and gentle rolls as it contours around the Cajon Pass drainage and heads east above Silverwood Lake. The landscape is characterized by sagebrush, scrub oak, and exposed granitic hillsides before beginning its upward pitch into the mountain front.

Lake Gregory Ascent — Miles 19.4–21.5

Turning off the highway onto Lake Gregory Drive, the road steepens considerably and the riding becomes significantly tighter. The open chaparral quickly gives way to dense stands of yellow pine, black oak, and mountain cedar as you climb toward the community of Crestline and the basin surrounding Lake Gregory.

Upper Rim of the World Highway — Miles 21.6–25.6

Joining CA-18, this section travels along the high southern escarpment of the range. Known as the Rim of the World Highway, the road hangs over steep canyon drops that fall away toward San Bernardino and the Santa Ana River valley below. Expect sweeping ridges, short rock-walled cuts, and frequent view pulls.

Arrowhead Basin Connector — Miles 25.7–27.6

A short transition onto CA-173 tracks into the shaded, wooded drainage surrounding Lake Arrowhead. Curves here are tight and sheltered under a thick tree canopy, with frequent side streets and localized mountain development.

High Crest Traverse to Big Bear — Miles 29.0–47.3

Back on CA-18, the route picks up a sustained climb east through Running Springs and up to the high alpine plateau. The road works through continuous S-curves and elevation climbs, carving through granite bluffs and dense timber. As you approach the 7,000-foot mark, the forest opens up near Big Bear Lake Dam.

Big Bear North Shore Drive — Miles 47.4–57.2

Branching onto CA-38 along the north shore of Big Bear Lake, the character shifts to a quieter, more relaxed pace. The road traces the contours of the lake through Fawnskin, framed by open pine forests and expansive water views across to the high peaks of the San Gorgonio Wilderness.

Big Bear City Valley Loop — Miles 57.3–62.5

Rejoining CA-18 briefly through Big Bear City, the route crosses the flat alpine valley floor. This short section serves as the geographic bridge between the Big Bear lake basin and the high mountain pass leading south.

Onyx Summit Pass & Mill Creek Canyon Descent — Miles 67.2–106.1

The final, longest segment on CA-38 begins with a steady climb out of the valley up to Onyx Summit, reaching the route’s high point at 8,448 feet. Beyond the pass, the road drops through the alpine meadows of Barton Flats before plunging into the tight, twisting gorge of Mill Creek Canyon. The descent drops nearly 6,000 vertical feet over 30 miles, ending at the canyon mouth near Mill Creek.

Seasonal & Environmental Context

Elevation on this route ranges from under 2,700 feet at Mentone to nearly 8,500 feet at Onyx Summit, creating substantial temperature gradients. A mild day in Cajon Pass or Mill Creek can turn bitterly cold near the high pass.

From late autumn through spring, snow and ice are common above 5,000 feet. Caltrans regularly enforces chain requirements or closes high sections of CA-18 and CA-38 during winter storms. Sand and volcanic cinders applied for winter traction often linger in shaded corners well into May. During summer and early autumn, afternoon heat builds on the lower desert and valley approaches, while monsoon thunderstorm activity can pop up quickly along the San Gorgonio ridge, bringing localized heavy rain and flash rockfall into Mill Creek Canyon.

Logistics & Services

Fuel, food, and supplies are concentrated in the mountain resort hubs along the crest: * Lower/Mid-Climb: Crestline and Lake Arrowhead (miles 20.0–27.0). * Central Crest: Running Springs (mile 35). * High Basin: Big Bear Lake and Big Bear City (miles 47.0–63.0).

Once you commit to CA-38 south of Big Bear City (around mile 65), there are no fuel stations for nearly 40 miles over Onyx Summit and down Mill Creek Canyon until you reach Mentone. Cell service can be spotty to non-existent through the depth of Mill Creek Canyon.

Important Considerations

Weekend Recreation Traffic: CA-18 and the roads around Big Bear Lake draw heavy traffic on weekends, including RVs, boat trailers, and day-trippers. Passing opportunities are limited to established turnouts and passing zones. * Pavement Surface Hazards: Shadowed, tree-covered corners around Lake Gregory and Lake Arrowhead can hold pine needles, dampness, and loose gravel even in dry weather. * Debris on Descents: The upper reaches of CA-38 and the steep walls of Mill Creek Canyon are prone to rockfall, particularly after rain or freeze-thaw cycles.