For your Onion Valley to Whitney trek via Kearsarge Pass, you've got some fantastic side hike options to consider! Matlock Lake is indeed a scenic detour, but if you're looking for more, Vidette Lakes offers a serene, less-trafficked spot that’s perfect for a peaceful camp. Wright Lakes is another great choice, especially if you're into high-altitude landscapes and solitude. If you're feeling ambitious, Mount Tyndall is a rewarding challenge with epic views. Arctic Lake is stunning and close to the main trail near Guitar Lake, so it’s worth a visit too. All these options provide beautiful, off-the-beaten-path experiences that are definitely worth structuring your campsites around.