The treaty led the U.S. government to contract for steamship service to Panama from ports on both coasts. When the California Gold Rush began in 1848, traffic through Panama greatly increased, and New Granada agreed to allow the Panama Railroad to be constructed by American interests. This first "transcontinental railroad" opened in 1850. There were riots in Panama City in 1856; several Americans were killed. US warships landed Marines, who occupied the railroad station and kept the railroad service from being interrupted by the unrest. The United States demanded compensation from New Granada, including a zone wide, to be governed by US officials and in which the United States might build any "railway or passageway" it desired. The demand was dropped in the face of resistance by New Granadan officials, who accused the United States of seeking a colony.