Historian Athelstan George Harvey [1884–1950] claims that the earliest description of Mount Robson (although not by its current name) is found in the journal of John M. Sellar, who passed the peak on August 26, 1862, as one of the “Overlander” party of gold seekers bound for the Cariboo:

At 4 p.m. we passed Snow or Cloud Cap Mountain which is the highest and finest on the whole Leather Pass. It is 9000 feet above the level of the valley at its base, and the guide told us that out of twenty-nine times that he had passed it he had only seen the top once before.

“Leather Pass” is Yellowhead Pass. Sellar’s journal is frequently referred to in The Overlanders of ‘62 (1931) by Mark Sweeten Wade [1859–1929], but the closest reference to the above quote I can find is:

Such [a guide] they found in a French half-breed named André Cardinal, a Freeman of the settlement of St. Albert, who was born at Jasper House, where he had spent the greater part of his life, and who had passed over the trail between Edmonton and his birthplace no fewer than twenty-nine times, and had also on several occasions made the trip between Jasper House and Tête Jaune Cache, on the Fraser River. They could not have secured a man better qualified to lead them successfully over the rough trails that now confronted them, and, as will develop later, one more trustworthy, resourceful, capable, and amiable. Cardinal agreed to conduct them to Tête Jaune Cache, and, if, as he expected they would do, they should find some Shuswap Indians encamped there, one of whom would guide them to Cariboo, he, Cardinal, would accompany the party as interpreter.

Margaret McNaughton [1856–1915], wife of one of the Overlanders, does not mention the mountain in her record Overland to Cariboo, 1896.

The British tourists and explorers William Wentworth Fitzwilliam Milton [1839–1877] and Walter Butler Cheadle [1835–1910] passed below Mount Robson in 1863:

A few hours’ travelling in the morning of the 14th [July 14, 1863] brought us to the Grand Fork of the Fraser, where an important branch from the north or north-east flows by five separate mouths into the main body of the Fraser, which we had been following thus far. Here we pulled up, in order to search carefully for safe fords by which to cross these numerous swollen streams. This Grand Fork of the Fraser is the original Tête Jaune Cache, so called from being the spot chosen by an Iroquois trapper, known by the sobriquet of the Tête Jaune, or “Yellow Head,” to hide the furs he obtained on the western side. The situation is grand and striking beyond description. At the bottom of a narrow rocky gorge, whose sides were clothed with dark pines, or, higher still, with light green shrubs, the boiling, impetuous Fraser dashed along. On every side the snowy heads of mighty hills crowded round, whilst, immediately behind us, a giant among giants, and immeasurably supreme, rose Robson’s Peak. This magnificent mountain is of conical form, glacier-clothed, and rugged. When we first caught sight of it, a shroud of mist partially enveloped the summit, but this presently rolled away, and we saw its upper portion dimmed by a necklace of light feathery clouds, beyond which its pointed apex of ice, glittering in the morning sun, shot up far into the blue heaven above, to a height of probably 10,000 or 15,000 feet. It was a glorious sight, and one which the Shushwaps of The Cache assured us had rarely been seen by human eyes, the summit being generally hidden by clouds.

James McEvoy [1862–1935] conducted a geological survey from Edmonton to Tête Jaune Cache for the Geological Survey of Canada in 1898:

Looking up Grand Fork is the most imposing view met with on the whole route. Great mountains are on every hand, but over all stands Robson Peak, “a giant amongst giants and immesurably supreme.” … The top of the mountain is usually hidden and rarely indeed is it seen entirely free from clouds. The actual height of the peak is 13,700 feet, or 10,750 feet above the valley. The face of the mountain is strongly marked by horizontal lines, due to the inequal weathering of the rocks, and has the appearance of a perpendicular wall. From the summit to the base on the Grand Fork, a height of over 10,500 feet, the slope is over 60 degrees to the horizontal. Although Robson Peak has been long known, its height had never been determined, nor was it supposed to be particularly notable in that respect, but now since the height of Mts. Brown, Hooker and Murchison have been proved to be greatly exaggerated, it has the distinction of being the highest known peak in the Canadian Rockies.

Arthur Philemon Coleman [1852–1939] visited the area in 1907 and 1908, writing several articles and producing a map of Mount Robson 1910

Arthur Oliver Wheeler [1860–1945] conducted a topological survey in 1912:

As a result of my trigonometric levels, the altitude of Mt. Robson is here computed at 13,068 feet. It is derived from transit readings taken at three distinct bench-marks at wide intervals apart-placed by the engineers of the Grand Trunk Pacific Railway-upon signals set on the adjacent peaks bordering the Fraser River Valley. The elevations derived were then carried from summit to summit to the highest point of the mountain. In one case the reading from the benchmark was directly upon the crest of Robson. The deduction is not absolute. It is impossible to make it so where no distinct signal, such as a rock cairn, has been sighted upon; and none can be placed on Robson, as the summit is covered by an immense snow cornice. Altogether, five sights were obtained on the crest from other summits, of which the altitude had been obtained through sighting on rock cairns built upon them, and one from the benchmark referred to. Two of these were discarded as uncertain, as they had been carried for long distances. McEvoy established a height for Mt. Robson of 13,700 feet, but do not think that any systematic series of observations were .employed by him. It is the fate of great peaks to have their reputed heights brought down, and fancy that more extended observations will find Robson no exception to the rule. The Massif with its glaciers and glacial lakes covers an area of over thirty square miles and measures three miles through at it base where it rises one and three-quarter miles into the air above the Grand Fork.

The Grand Trunk Pacific Railway passed through the Yellowhead Pass around 1911. William Pittman Hinton and G. T. Bell and publishbed a promotion in the 1909 Canadian Alpine Journal:

Although Robson Peak has been long known its height had never been determined until recently, nor was it supposed to be particularly notable in that respect, but now since the height of other mountains in the Rockies which were considered to be the highest in Canada have been proved to be greatly exaggerated, Mt. Robson has the distinction of being the highest known peak in the Canadian Rocky Mountains, and will be owing to its magnificent surroundings, one of the greatest attractions of the Grand Trunk Pacific for tourists and alpine climbers, and as one mountain climber who has made two attempts to ascend this mountain, has said, “It will be the show place of the world.” The mountain is easy of access, within a few miles of the Grand Trunk Pacific track.

James Monroe Thorington [1895–1989] summed up the results of the Alberta-British Columbia Boundary Commission

Mount Robson is the highest summit in the Rockies of Canada; but, like many a lesser peak, its height has diminished with recent measurements. The first triangulation, that of McEvoy, resulted in a figure of 13,700 feet; but the more recent determination of the Interprovincial Boundary Commission has brought this down to 12,972 feet. Thus an old illusion is shattered, and no peak of the Rockies of Canada attains thirteen thousand feet.