The Walla Wallas eventually adopted maintaining cattle herds, going as far as New Helvetia in California during 1844 to secure additional livestock. An estimated 40 Walla Wallas, Nez Perce and Cayuse under Walla Walla chief Piupiumaksmaks went on the expedition south. En route the party gathered stray horses, not aware the strays were stolen. Negotiations at New Helvetia were held between one of Piupiumaksmaks' sons, Toayahnu, and an employee of Sutter. The two men entered a dispute, and Toayahnu was killed. Despite fears of retribution among Sutter's staff by the Walla Wallas, Piupiumaksmaks returned with a small band of warriors and families in 1846 and declared peaceable intentions. The returning party had members infectees of measles, which began to spread across the Columbia Plateau, decimating indigenous populations. Smallpox and other diseases were also introduced into the area, increasing the Walla Wallas population decline. Despite this, the Walla Wallas then held extensive herds of horses, being the "principal wealth" of the tribe.