Probably the most direct route from Salt Lake City would be Interstate 80 to Reno, Highway 395 to Susanville, Highway 44 to Redding and Interstate 5 to Medford.
If you are coming from Boise, and if the weather is poor, Interstate 84 through the gorge to Portland and I-5 south would be safest. A beautiful and direct route if snow and ice over the passes are not a threat would be I-84 to Ontario, Highway 20 to Salem and I-5 to Medford.
If you're not in a hurry, and the weather is favorable, there are many alternate routes through that beautiful country.
Margi