There are several routes from Riverside into the Southern Sierra Nevada/Kern River Valley areas.
Hwy 395 (blue line) to Hwy 58 at Kramer Junction. This section of Hwy 395 is in the Western Mojave Desert (presence of Joshua Trees) and I include a few flowers seen along that road.
Hwy 58 (gold line) from Kramer Junction west passes through Tehachapi. Then, Caliente-Bodfish Road [Kern County Road 483] takes us north to Lake Isabella, and into Kernville, then following the Kern River up to Johnsondale (green line).
Another route is to continue on Hwy 395 north from Kramer Junction to Hwy 178 (red line) just north of Ridgecrest. Hwy 178 goes west through the western Mojave Desert across Walker Pass towards Lake Isabella. A few miles before at Weldon, Sierra Way goes north, following the Kern River into Kernville.
A popular return route is via Sherman Pass Road (black line) over the Pass (Elevation 9200') and down into Kennedy Meadows and the Wilderness Areas, connecting with Hwy 395.