Yosemite National Park is quite possibly the easiest place in the world to hitchhike in/around. As the central valley is absolutely terrible for hitchhiking in, it is strongly recommended to take public trasportation to a "gateway city" (i.e. Merced, Fresno, Modesto), and then hitch from there [incidentally, I prefer Merced, as it is the least sketchy of these few cities]. Once in the park, getting around shouldn't be a problem. When in Yosemite Valley, the easiest place to get rides around and out of the park is Camp 4 on the valley's west side. Here, all traffic will be leaving the valley. The Major Highways emminating from Yosemite Valley are 41, 140, and 120. Highway 41 will take you to Wawona, Oakhurst, Fresno, etc... 140 will get you to El Portal, Mariposa (you don't want to end up there), Merced (and from there to Santa Cruz)... 120 can take you to Modesto, the Bay Area, and east to Tuolumne Meadows, Lee Vining, Mammoth, etc. The best way to hitch here is to plan on getting several rides. All highways in Yosemite Valley are connected for a good 5 miles, so if you want to go down 120 to San Francisco, and someone stops and say their going to Fresno, ask him to take you to where 41 turns off of 120.