The spatial distribution of the young objects of varioue age groups -
HII regions and open clusters - in the Saglttarius-Carina arm (SC arm) at 1 « 280°- 25° ie Inyestlgated. Both transverse and longitudinal age gradients have been found in the arm, Two giant star formation complexes with the size of about 1 kpc at 1 = 285°-300° at 1 = 340°-20° are existed, Each of them contains several giant HII regions, a number of glant moleoular clouds (GMCa) and some extremely young clusters, Between these complexes we have found an elder one of the same aime.This complex contains 24 (3-6)»10^7 years old clusters and a small number of faint HII regions. Assuming that it is a remnant of a
giant star formation complex the upper limit of lifetimes for such complexes and GMCs is (3-6)•10^7 years,
The estimations of spiral pattem parameters are made.The value of the pitch-angle is 21°+3°. The value of spiral pattem velocity, -26.8+2.2 km/s«kpc, leads us to conclusion that the Sun is near the oorrotation radius of the Galaxy. The star formation efficiency in
these complexes is discussed.