Complex sentence: In 1874 aboard the Coast and Geodetic Survey schooner "Yukon", he anchored in Lituya Bay, which he compared to Yosemite Valley (California), had it retained its glaciers.
Split into simpler sentences: In 1874 aboard the Coast and Geodetic Survey schooner Yukon, he anchors in Lituya Bay. He compared it to Yosemite Valley (California), if it would had retained its glaciers.