For at least part of that time, Ehrenberg lived in La Paz. Some historians, such as Ornish, maintain that in 1846 and 1847 Ehrenberg sailed to Tahiti and several other Polynesian islands. Some historians report that in 1846 Ehrenberg joined the 1st Regiment of New York Volunteers in California to fight in the Mexican–American War. Most evidence disputes that Ehrenberg actually joined the army. According to the memoirs of one of the soldiers in that unit, Ehrenberg was a civilian and "volunteer aide" to Captain Seymour Steele of that regiment. In March 1848, Ehrenberg and 33 other men rescued American prisoners held south of La Paz. In January 1854, California residents learned that the Gadsden Purchase had been completed. Charles Poston recruited prospectors, including Ehrenberg, to travel to the new area and see what mining opportunities existed in the region. The group intended to sail aboard the "Zoraida" to Guaymas, Mexico, then travel overland to Tucson. The "Zoraida" was shipwrecked just off the coast of Mexico, and Ehrenberg and his comrades were stranded on a small island which had fresh water and wild cattle. The men constructed a raft and sailed to the mainland, where they continued on their journey. They were briefly imprisoned when Mexican authorities mistook them for filibusters following William Walker in trying to take Baja California. The group reached Tubac, Arizona and soon gathered samples of gold, silver, and copper. Much of this was likely acquired from other miners. Ehrenberg and Poston took the samples overland to San Francisco to gain investors for a mining consortium. On the way, the men stopped near Fort Yuma and Ehrenberg surveyed a townsite, which he called Colorado City. The site eventually became the town of Yuma; Ehrenberg saw no profit from it. In 1856 he partnered with Charles Poston to form the Sonoro Exploring and Mining Company. From 1863 through 1866, Ehrenberg served as Indian Agent for the Mojave people at the Colorado River Indian Reservation. In 1865, Ehrenberg was a member of the convention held in Tucson in August 1856 requesting that the United States Congress organize the territory of Arizona. Ehrenberg contributed to "Mining Magazine", the "Journal of Geology", and "Arizona Weekly". Ehrenberg was murdered on October 9, 1866 in Dos Palmas, California, a stop on the Bradshaw Trail.