A survey marker, placed by the U.S. Army Corps of Engineers Sacramento District, designates an inventoried tree along the American River near Watt Avenue in Sacramento, Calif., Jan. 4, 2012. Trees identified in the survey were marked or tagged to signify that they were included in the inventory. GPS coordinates were recorded for each item identified, allowing engineers to eventually create virtual models of the levees. The study is part of the district’s American River Common Features project, a partnership with the Central Valley Flood Protection Board and the Sacramento Area Flood Control Agency to improve levees and reduce flood risk for the city.