As a guide, Gaspard's two most important customers were Emmanuel Boileau de Castelnau and Henry Duhamel. A turning point for Gaspard was his first meeting with Boileau de Castelnau in 1876. The Huguenot nobleman of Languedoc liked the modest mountaineer so much that he greatly extended his stay in the mountains. With Boileau de Castelnau, Gaspard formed one of the most brilliant ropes of their era, making a dozen first ascents in the 1876 and 1877 seasons. By hunting for chamois, Gaspard became aware of a number of routes to less prominent peaks and passes. On 21 July 1877, Gaspard and Boileau de Castelnau made the first ascent of the Dôme de Neige () in the Massif des Écrins Barre.