Rookery Falls is 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, extending 14 miles (22.5 km) northeast from Whittier to the south end of Port Wells. It was named in 1794 by Captain George Vancouver, presumably because it 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 onto the North American Plate. The Chugach Mountains, on the north side of Passage Canal, are mostly sedimentary and metamorphic, consisting predominantly of sandstone with layers of calcite and phyllitic schist. The Kenai Mountains, on the south side of the fjord, are composed mainly of Cretaceous-age slates, sandstones, and greywackes. During the Pleistocene glaciation, a series of ice advances repeatedly buried Passage Canal. Several small glaciers, remnants of these ancient ice streams, remain in the Portage Pass area. The largest is Portage Glacier, in the Kenai Mountains, with a catchment area of about 10,240 acres (4,144 ha). Today, it drains into Turnagain Arm. Whittier Glacier, also in the Kenai Mountains, has a catchment area of about 5,120 acres (2,072 ha) and a maximum length of 1.7 miles (2.7 km). Its terminus, at an elevation of about 1,700 feet (518 m), is above the town of Whittier and drains into Passage Canal. Learnard Glacier originates in the Chugach Mountains and flows south for about 2.4 miles (3.9 km) to its terminus at 800 feet (244 m), then drains to tidewater in Passage Canal.

Historical accounts provide descriptions of trails that linked people of the southern Kenai coast with resources and trading partners in Cook Inlet and Prince William Sound. In 1794, Captain George Vancouver recorded information from Russians sources about a trade route near Portage Valley that crossed the isthmus between Cook Inlet and Prince William Sound. Lieutenant Joseph Whidbey led an expedition to locate the trail from Passage Canal, but although he did not find it, he discovered a house built in the Russian style at the head of the fjord. Its location suggested that the isthmus was not only passable but frequently traversed. By the late 1890s, the U.S. government and military had begun investigating trails on the Kenai Peninsula. In 1898, Lieutenant H.G. Learnard of the US Army 14th Infantry was tasked with surveying and exploring the region, focusing on Alaska Native trails and portages. The U.S. Army sought firsthand information on existing routes to forts and potential pathways for miners and prospectors. Learnard’s party included Captain Howe and his son, Corporal Young, seven enlisted men, Luther ‘Yellowstone’ Kelly, and Walter C. Mendenhall, a geologist with the US Geological Survey. They crossed the peninsula from Passage Canal in Prince William Sound, over Portage Glacier, to Turnagain Arm. As late as 1914, it was still possible to travel from Passage Canal through Portage Pass into Portage Valley via a trail over Portage Glacier. By 1939, however, glacial recession and ablation had rendered this route impassable in summer. A US Geological Survey party that year encountered numerous large crevasses and serac ice, as well as unscalable cliffs. To cross from Passage Canal to the Portage Creek valley, they had to ascend 3,000 feet (914 m) to the summit of a ridge. Today, the Portage Pass Trail is a popular 2-mile (3.2 km) hike. It begins at the head of Passage Canal, climbs 750 feet (229 m) to the pass, and descends to a gravel beach at Portage Lake. As Portage Glacier retreated, the lake has expanded, severing the trail’s connection to Portage Creek valley. However, the pass remains an important migratory route for birds.

Rookery Falls is named for a large rookery adjacent to the waterfall, home to about 6,000 breeding black-legged kittiwakes, as well as glaucous-winged gulls and pigeon guillemots. This is one of the largest kittiwake colonies in Alaska and is accessible only by boat. The black-legged kittiwake is a small gull that nests on narrow cliff ledges, either on offshore islands or in inaccessible areas of the coastal mainland. Often, the ledges are barely wide enough to hold a nest. Adults and chicks must sit facing the cliff, with their tails hanging over the edge. Nests are made of seaweed, grass, feathers, and mud, which cements the materials together. Kittiwakes are colonial nesters, with colonies ranging from a few nests to thousands. Nests are often so close together that they touch. In Alaska, black-legged kittiwakes nest from Point Hope on the Chukchi Sea, throughout the Aleutian Islands, and across much 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 rarely ventures far from the ocean. It is found along the Pacific coast from western Alaska to Washington. This species regularly hybridizes with the American herring gull in southern Alaska, producing a hybrid sometimes referred to as the Cook Inlet gull. This hybrid population can be found from Alaska to southern California. In western Alaska, hybrids with glaucous gulls are common, making up as much as 50% of the gull population on the Seward Peninsula. The pigeon guillemot is an alcid in the auk family of seabirds, found in North Pacific coastal waters from Siberia to California. It breeds and roosts on rocky shores, cliffs, and islands near shallow waters. In winter, some birds move slightly south in the northernmost part of their range in response to advancing ice, while others migrate slightly north in the southern part of their range, generally favoring more sheltered areas. Pigeon guillemots feed on small fish and marine invertebrates, mostly near the seafloor, catching prey by pursuit diving. They are monogamous breeders, nesting in small colonies close to the shore. Each pair defends a small territory around a nesting cavity, where they lay one or two eggs. Both parents incubate the eggs and feed the chicks. Once fledged, the young bird is completely independent of its parents. Read more here and here. Explore more of Rookery Falls and Passage Canal here: