We present a large-scale mapping toward the GEM OB1 association in the galactic anti-center direction. The 9 degrees x 6 degrees.5 area was mapped in (CO)-C-12, (CO)-C-13, and (CO)-O-18 with similar to 50" angular resolution at 30" sampling. The region was divided into four main components based on spatial distribution and velocity: the Gemini OB1 Giant Molecular Cloud (GGMC) Complex, the Lynds Dark Clouds and the West Front Clouds, the Swallow and Horn, and the Remote Clouds. The GGMC Complex is located in the Perseus arm, while the Lynds Dark Clouds and the West Front Clouds are located in the Local arm. Swallow and Horn are revealed for the first time in this paper. The two clouds have a similar velocity interval ([11, 21] km s(-1)) and have similar sizes (0.6 and 0.8 deg(2)). We analyzed the structure of these clouds in detail and calculated their parameters (mass, temperature, etc.). Two elongated structures were discovered in a longitude-velocity map in the velocity interval [11, 30] km s(-1). We also found an interesting filament that shows a 0.8 km s(-1) pc(-1) gradient perpendicular to the direction of the long axis.