The Union Line was a transport company of steamboats of the Colorado River, owned by Thomas E. Trueworthy, operating in southeastern California, western Arizona Territory, and northwestern Mexico.
Merchants and miners held a protest meeting at La Paz, Arizona on December 1, 1863, fed up with shortages, delayed and slow deliveries of freight to their stores and mines, by Johnson & Company, who owned the Colorado River's only two steamboats.
The meeting voted to send a representative to San Francisco with a petition calling for the establishment of an opposition steamboat line on the Colorado River.
In San Francisco, their representative Samuel "Steamboat" Adams convinced the Chamber of Commerce to endorse an opposition line.
Merchants of the city raised $25,000 by subscription, and Adams persuaded Captain Thomas E. Trueworthy, to send the Sacramento River steamboat Esmerelda under Captain Charles C. Overman and the Victoria, a four-masted schooner converted from a barge, to the Colorado River to establish the Union Line there.