The island is geographically distinctive as it was formed by post-glacial rebound with the retreat of the last ice age. Before the arrival of European settlers, the island was inhabited by the Pentlatch, a Coast Salish First Nations band who called the Island Ja-dai-aich, meaning The Outer Island. The island was found and named Isla de Lerena during the 1791 voyage of the Spanish ship Santa Saturnina, under Juan Carrasco and José María Narváez. The name honors the Spanish Finance Minister, Don Pedro López de Lerena, Count of Lerena, who supported the movement of Spanish Ships over there. In 1850 the British renamed it after Rear Admiral Phipps Hornby, then Commander of the Pacific Station.

Hornby Island is mostly covered by mixed forest dominated by Douglas-fir. Western red cedar, western hemlock, grand fir and lodgepole pine are the other large conifers present. The smaller Pacific yew is scattered in the understorey. The arbutus, a broadleaf evergreen species, is plentiful. Broadleaf deciduous trees include bigleaf maple, red alder, black cottonwood, Pacific flowering dogwood, cascara and several species of willow. Populations of Garry oak occur on the southern end of the island and at Helliwell Provincial Park. Only about 260 acres (1.1 km²) of undisturbed stands for older forest have been identified on Hornby Island, which amount to roughly 3.5% of the island's area. There are roughly 1,330 acres (540 ha) of older second-growth stands on the island, which amount to 19% of the island.^[2]

The island's soils have developed from marine deposits of variable texture, except for the higher elevations and steeper slopes where weathered clastic sedimentary rock provides the parent material. Most of Hornby's soils are sandy or gravelly, but some deep black loams occur in the northwestern part and many of the sands at the southern end have loam-textured topsoils. Podzols are common and the bleached sand grains associated with their eluvial (A₂, Ae or E) horizons lend a salt-and-pepper appearance to many forest trails. In most cases, though, the E is not very thick and may be discontinuous. On this account, the soils were mostly classified as Brown Podzolic in a soil survey published in 1959. All of the island's soils are strongly acidic in their natural state except for those which have developed on shoreline shell middens.^[3]

The Late Cretaceous Northumberland Formation is exposed in the northern and western part of the island. Fossil collectors have found ammonite and baculite fossils at Boulder Point on Hornby Island.^[4] A species of saurodontid fish (previously considered a pterosaur) called Gwawinapterus was identified based on a fossil found on a beach on Hornby Island.^[5] An actual azhdarchoid pterosaur was later identified from the formation, as well as Maaqwi, an early aquatic bird.^[6][7] An incredibly diverse shark community is recorded in shark teeth fossils from the area.^[8]

• Hornby Island Bus
• Hornby Island Commerce Website
• Hornby Island Co-op Store
• Hornby Island Residents' & Ratepayers' Association
• 2006 census data
• 2016 census data
• 2021 census data
• Helliwell Provincial Park
• Tribune Bay Provincial Park

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