On September 1, 2011, about 1725 central daylight time, a Bombardier CL-600-2B19 airplane, N875AS, operated as Delta Connection flight 5058, landed at the Baton Rouge Metropolitan Airport (BTR), Baton Rouge, Louisiana, with the left main landing gear in the retracted position. The airline transport pilot captain, first officer, flight attendant, and 50 passengers were not injured. The airplane received minor damage. Visual meteorological conditions prevailed for the landing and an instrument flight rules flight plan was filed for the 14 Code of Federal Regulations Part 121 flight. The flight originated from the Hartsfield Jackson Atlanta International Airport (ATL), Atlanta, Georgia, at 1409. While configuring the airplane for landing, the flight crew observed a landing gear disagree message, and the left main gear indicated that it was not down and locked. The Quick Reference Handbook (QRH) procedures were accomplished, which included cycling the landing gear handle and the use of the alternate gear extension (manual release) system; however, the crew was unable to get the left landing gear to extend. The captain declared an emergency and elected to land the airplane with the right main landing gear and nose gear extended. The airplane came to rest in an upright and left wing low position. The captain commanded an evacuation, and all passengers departed the airplane using the left forward door. Post-incident inspection of the airplane revealed minor damage to the left wing. There was no other damage to the airplane as a result of the left main landing gear being retracted at the time of landing. Examination of the left main landing gear assembly revealed that the upper attachment bolt for the left main landing gear uplock assembly, which is designed to be attached to both the uplock mechanism and the structure, was attached to the airplane structure only. Maintenance had been performed on both the left and right main landing gear systems prior to the incident flight. The mechanic who performed the maintenance did not have prior experience performing the installation of the uplock assembly. Following the incident, Atlantic Southeast Airlines changed their maintenance requirements and procedures to prevent future accidents. In addition, Bombardier issued Service Letter ATA:3230 to address this maintenance discrepancy and prevent future accidents.