[2][self-published source] During his first voyage to the northwest coast, Gray was second-in-command of Columbia Rediviva under Captain John Kendrick, who remained in the Pacific, in command of Lady Washington.

[2][self-published source] In October Columbia Rediviva and crew began building Fort Defiance and a small craft called Adventure as they prepared to ride out the winter in harbor.

[2][self-published source] On this journey aboard Columbia Rediviva Gray noticed muddy waters flowing from shore and decided to investigate his belief that it might be the "Great River of the West".

This ship was HMS Discovery commanded by British naval captain George Vancouver, who doubted that Gray had found a navigable river-mouth.

[2][self-published source] The several large rivers and capacious inlets that have been described as discharging their contents into the Pacific between the 40th and 48th degree north latitude, were reduced to brooks insufficient for our vessels to navigate, or to bays inapplicable for refitting.

Gray informed Vancouver at this chance meeting that he had located a large river at the latitude of 46'10" but had been unable to enter it due to the outflow.

[6][7]So Gray informed Vancouver that he would further investigate that area, and then sailed south after several more days near the Strait of Juan de Fuca.

This time he ordered a small sailboat launched to attempt to find a safe passage across the sand bars in the process known as sounding.

[2][self-published source] Finally in the evening of May 11, 1792, Gray's men found a safe channel, and so ship and crew sailed into the estuary of the Columbia River.

Trading with the locals consisted mainly of exchanging nails and other small iron products for pelts, salmon, and animal meat such as deer and moose.

[14][page needed] Gray "landed on the north riverbank, raised the American flag, planted some coins under a large pine tree, and claimed possession for the United States.

[18] However, before Gray and his crew sailed for China, they returned to Nootka Sound where he passed along news of his discovery to the Spanish commandant there, Quadra.

[19] Gray left with Quadra a chart and description of the river's mouth that Captain Vancouver obtained a copy of in September.

[11][page needed] A short time after entering the Columbia River and trading with the natives, ship and crew sailed to China to sell the pelts[2][self-published source] before returning to Boston in July 1793.

Present day Astoria, Oregon, where John Jacob Astor would establish his trading post less than 20 years after Gray's discovery, is situated on the south shore of the Columbia estuary.

[25] In 1775, Spaniard Bruno de Heceta (also spelled Hezeta) was exploring the northwest coast of North America with the vessels Santiago and Sonora under his command.

[27] Captain John Meares, during his 1788 exploration of the Pacific Northwest, had on board a copy of a Spanish map made by Francisco Antonio Mourelle and Juan Francisco de la Bodega y Quadra which showed the Columbia River's mouth as Entrada descubierta por Dn Bruno Hezeta.