General Motors GM EMD GT-22 Diesel Electric Train Engine - Línea San Martín - LSM (Palermo, Buenos Aires)
Credit goes to Raúl Alejandro Rodríguez for identifying this locomotive.
Here is what he wrote:
This photo is of one of the little batch of GM EMD GT-22 imported from the U.S.A. as she has the hooks to be lifted by the cranes that take it from the ship and put it in Argentine rails. The great batch built in Argentina doesn't have the hooks.
The ALCO RSD-16 was an export model. It was basically an RSD-12 but with 6 axles and a four stroke diesel engine (the 1800 HP Alco 251). The Alco locomotives where acquired in 1957 and (among other lines) where put in service in the suburban section of the Ferrocarril General San Martín. But by the seventies they where supplemented with the General Motors GM EMD GT-22 locomotives (2200 HP two strokes diesel engines). Most of them where built under license by Astarsa in Argentina. From some 10 years ago also a few second hand ex Renfe series 319 Alcos were seen in front of those suburban trains. By now there are no GM nor Alcos as they were all replaced by new Chinese locomotives CSR SDD7.- Note that the Alco locomotives are taller than the GMs and that the GMs are longer than the Alcos. The GMs have the cabin in one end of the locomotive as the Alcos have the cabin not in the middle but near one end so they have one long hood and other shorter. This photo (PHOTO ID 478407) is a good shot of the two types of locomotives (left the GM and right the ALCO) in the colours of Linea San Martín.
For more information about the EMD GT22, read en.wikipedia.org/wiki/EMD_GT22_Series.