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Both Yosemite and Death Valley are open in March, but Tioga Pass is closed for winter. That would make it tough to see both in just 2 days. The coast highway, Sequoia or even Lake Tahoe would be a couple other popular options. Just keep in mind that it is already a full day drive going to most direct route, so by the time you add in any one of them, will pretty much fill up all your extra time.