Poison Oak is mostly a western state bush or small tree that flourishes in the foothills usually below major snow line/freeze zone; poison ivy is not in Cali unless someone recently introduced it.
Many years ago there were few options to combat the itching. the best thing available then was Fells Naphtha bar soap – bodies and clothing.
Speaking from personal experience, best advice is when out of poison oak territory, all equipment must be washed clean or neutralized (including redbags, vehicles, etc if anyone will be “tinkering” with them later). humans should seek medical intervention to start a series of inoculations to hopefully prevent future allergic reactions next season.