Hi, my first post--
The best day hike that I hike is the Tuolumne Meadows trail in the High Sierras of Yosemite. Take the path towards Glen Aulen (a High Sierra Camp.) You can go to the camp or just to the Cascades and back. It's spectacular--mountains, forest, river, meadows, cascades...all in one easy hike and doable in about 4 hours total.