We present the first paper in a series detailing the results of (CO)-C-13 observations of a similar to 1 deg(2) region of the giant molecular cloud (GMC) complex associated with the H II region RCW 106. The (CO)-C-13 observations are also the first stage of a multimolecular line study of the same region. These observations were amongst the first made using the new on-the-fly mapping capability of the Australia Telescope National Facility Mopra Telescope. In the configuration used, the instrument provided a full width at half-maximum (FWHM) beam size of 33 arcsec and a velocity resolution of 0.17 km s(-1). The gas emission takes the form of a string of knots, oriented along an axis that extends from the north-west (NW) to the south-east (SE) of the field of the observations, and which is surrounded by a more extended, diffuse emission. We analyse the 2D integrated (CO)-C-13 emission using the CLUMPFIND algorithm and identify 61 clumps. We compare the gas data in the GMC with the dust data provided by 21-mu m Midcourse Space Experiment (MSX) and 1.2-mm Swedish European Southern Observatory Submillimetre Telescope (SEST) images that we both regridded to the cell spacing of the Mopra data and smoothed to the same resolution. The (CO)-C-13 emission is more diffuse and extended than the dust emission revealed at the latter two wavebands, which both have a much higher contrast between the peaks and the extended emission. From comparison of their centre positions, we find that only similar to 50 per cent of the (CO)-C-13 clump fits to the data are associated with any dust clumps. Using the clump fits, the total local thermodynamic equilibrium gas mass above the 3 sigma level measured from the molecular data is 2.7 x 10(5) M-circle dot, whereas that measured from the smoothed 1.2-mm SEST dust data is 2.2 x 10(5) M-circle dot.