Rookery Falls is located on the northern shore of Passage Canal in Prince William Sound, about 50 miles (80 km) southeast of Anchorage and 1.7 miles (1.9 km) north-northeast of Whittier, Alaska. The waterfall is about 200 feet (61 m) high and drains a small lake perched above the cliffs. Passage Canal is a fjord on the northeast coast of the Kenai Peninsula that trends northeast for 14 miles (22.5 km) from Whittier to the south end of Port Wells. Passage Canal was named in 1794 by Captain George Vancouver, presumably because the fjord leads to an ancient trail over Portage Pass. The basement rock surrounding Passage Canal belongs to the Valdez Group, a belt of Cretaceous and Jurassic terrane that accreted against the North American Plate. The rocks of the Chugach Mountains, on the north side of Passage Canal, are mostly sedimentary and metamorphic rocks, predominantly blocks of sandstones with layers of calcite and phyllitic schist. The rocks of the Kenai Mountains, on the south side of Passage Canal, are mostly slates, sandstones, and greywackes of Cretaceous age. Portage Pass was overridden by a vast mass of ice that buried all but the highest peaks during the Pleistocene glaciation. The ice mass flowed out of the Kenai and Chugach Mountains toward Portage Pass and then divided, with one ice stream flowing northeastward to what is now Passage Canal, and another flowing northwestward down Portage Valley to Turnagain Arm. Several small glaciers that are remnants of the greater Pleistocene glaciers are still found in the Portage Pass area. The largest of these is Portage Glacier, which has a catchment area of about 10,240 acres (4,144 ha) and a length of about 4 miles (6 km). This glacier starts in the Kenai Mountains about 5 miles (8 km) south of Portage Pass and flows generally northward to Portage Lake. Whittier Glacier has a catchment area of about 5,120 acres (2,072 ha) and a maximum length of about 1.7  miles (2.7 km) and is perched above the town of Whittier where the terminus is at an elevation of about 1700 feet (518 m). Learnard Glacier is about 2.4 miles (3.9 km) long and the terminus is at an elevation of 800 feet (244 m) and about 0.8 miles (1.3 km) from tidewater. There are also several smaller glaciers and permanent snowfields in the area of Portage Pass, but none of these presented a substantial obstacle to Alaska Natives, Russian fur traders, and early settlers who used an ancient trail across the pass connecting Passage Canal with Turnagain Arm.

Historical accounts of the coast provide evidence of land use and the presence of people and their activity. Descriptions of trails that linked people of the southern Kenai coast with resources and trading partners in Cook Inlet and Prince William Sound were known by early explorers. In 1794, the journals of Captain George Vancouver recount information learned from Russians about a trade route near Portage Valley used to cross the isthmus between Cook Inlet and Prince William Sound. Lieutenant Joseph Whidbey led an expedition to investigate the trail from Passage Canal, and although he didn’t find the trail, he did find a house at the head of the fjord built in the Russian style with logs and ascertained, based on the location, that crossing the isthmus was not only possible but frequently done. In the late 1890s, the U.S. government and military began to investigate trails on the peninsula. In 1898, Lieutenant H.G. Learnard of the U.S. Army 14th Infantry received instructions to inventory and explore sections of the Kenai Peninsula that interested the military The U.S. Army needed first-hand information especially on Alaska Native trails and portages to learn of routes to existing forts and to identify other routes that could be used by miners and prospectors entering the region. Learnard’s party consisted of Captain Howe and his son, Corporal Young, seven enlisted men, Luther ‘Yellowstone’ Kelly, and Walter C. Mendenhall a geologist with the U.S. Geological Survey. The party crossed the peninsula from Passage Canal in Prince William Sound, over Portage Glacier, to Turnagain Arm. In 1914, it was still possible to cross from Passage Canal through Portage Pass to Portage Valley by way of a trail over Portage Glacier, but by 1939, glacial recession and ablation had made this route impracticable for summer travel. Because of the numerous large crevasses and serac ice on the surface of the glacier and the unscalable cliffs, a U.S. Geological Survey party in 1939 found it necessary to climb 3,000 feet (914 m) to the summit of a ridge to cross from Passage Canal to the Portage Creek valley. Today, the trail is a popular hike of about 2 miles (3.2 km) that starts at the head of Passage Canal and climbs 750 feet (229 m) to the pass and then descends to a gravel beach at Portage Lake. The lake has grown as the Portage Glacier retreated and the trail no longer connects with the Portage Creek valley; however, the pass is used as a migratory route for birds.

Rookery Falls is named after a large rookery adjacent to the waterfalls that has about 6,000 breeding black-legged kittiwakes, in addition to glaucous-winged gulls and pigeon guillemots. This is one of the largest kittiwake colonies in Alaska and is only accessible by boat. The black-legged kittiwake is a small gull that nests on narrow cliff ledges on offshore islands or inaccessible areas of the coastal mainland. Often the ledges are barely wide enough to fit a nest. The adult and chicks must sit on the nest facing the cliff with their tails hanging off the edge. Nests are composed of seaweed, grass, feathers, and mud to cement them together. Kittiwakes are colonial nesters and colonies may vary from a few nests to many thousands. Frequently, nests are so close together that they are literally touching. In Alaska, black-legged kittiwakes nest from Point Hope on the Chukchi Sea, in the Aleutian Islands, and east throughout most of the Gulf of Alaska including Cook Inlet, Prince William Sound, and Southeast Alaska. The glaucous-winged gull is a large, white-headed gull that is rarely found far from the ocean. It is a resident from the western coast of Alaska to the coast of Washington. This species hybridizes regularly with the American herring gull in southern Alaska, sometimes referred to as the Cook Inlet gull. This hybrid combination may be found along the Pacific coast from Alaska to southern California. Hybrids with glaucous gulls are common in western Alaska where up to 50% of birds on the Seward Peninsula are hybrids. The pigeon guillemot is an alcid in the auk family of seabirds, found in North Pacific coastal waters, from Siberia through Alaska to California. The pigeon guillemot breeds and sometimes roosts on rocky shores, cliffs, and islands close to shallow water. In the winter, some birds move slightly south in the northernmost part of their range in response to advancing ice and migrate slightly north in the southern part of their range, generally preferring more sheltered areas. Pigeon guillemots feed on small fish and marine invertebrates, mostly near the seafloor, that are caught by pursuit diving. They are monogamous breeders, nesting in small colonies close to the shore. They defend small territories around a nesting cavity, in which they lay one or two eggs. Both parents incubate the eggs and feed the chicks. After leaving the nest the young bird is completely independent of its parents. Read more here and here. Explore more of Rookery Falls and Passage Canal here: