Jedediah Smith was likely the first non-Indian to pass through Mechoopda country, in January and April of 1828, although there is no evidence they had contact. From 1828 to 1836, members of the Hudson Bay Company trapped the waters of the region, and it is likely the Mechoopda were at least aware of their presence. One of the early effects of groups such as the Hudson Bay Company may have been the large number of game in which they killed, resulting in a fairly rapid depletion of the large mammal population. For example, in January of 1833, members of the company under Michael La Framboise camped in the Sutter Buttes to take refuge from local flooding. While there they reported killing 395 elk, 17 bears, and 8 antelope.
In 1833, an epidemic thought to be malaria, entered the northern Sacramento Valley with stunning, lethal results. Some areas may have suffered mortality rates of 75%. The effect of this epidemic on the Mechoopda is unknown, although they were clearly in its path.
In 1844, Governor Micheltorena issued a series of land grants, including the Rancho Arroyo Chico grant to William Dickey in the fall of 1845. This grant was later purchased by John Bidwell. The area encompassed by the Rancho Arroyo Chico grant, as well as the Esquon grant, included the lands occupied by Mechoopda. With the establishment of the ranchos, the introduction of agriculture and cattle, local native people soon entered into a working relationship with the newcomers as ranch hands.
With the discovery of gold in January of 1848, and the literal invasion of their country by tens of thousands of miners, merchants, and immigrants from around the world, the lives of native people were forever altered, and would quickly reach a point when their very survival would be questioned. Ironically, many of the Mechoopda participated in the mining of gold, accompanying John Bidwell to the Feather River at a place which became known as Bidwell Bar. Bidwell's native laborers helped him extract some $100,000 in gold between 1848 and 1849, for which they were compensated in trade goods such as handkerchiefs, cigars, scissors, brandy, glass beads and pants.
The discovery of gold in California resulted in major changes to native societies like Mechoopda. With the massive influx of immigrants, access to the range of traditional foods necessary for survival became much more limited. Indians often met with violence in efforts to hunt and gather in accustomed places. Mining also resulted in serious environmental damage, such as the silting of streams, which damaged crucial salmon runs. Even the course of Little Butte Creek, upon which the village of Mechoopda rested, was altered after a build-up of deposits from dredging gold upstream blocked its normal flow, diverting the stream into another channel. Most markedly, these series of changes forced the Mechoopda and other native people out of a hunting and gathering economy into the cash economy, very quickly. People had to learn new skills, a new language, and adapt to new foods as matters of immediate survival. Between 1848 and 1850 the world must have seemed as though it had turned upside down.