It's probably dispatched on another group, and only used in times when there's so much traffic that they need to 'split' that division off, dispatch-wise.
Just to check, though I haven't run the trunk monitor in some months on the SD City Trunk here's channel 'hits' cumulative for the various dispatch groups I have monitored:
1296 - Southern Dispatch 1 : 61991 hits
1360 - Southern Dispatch 2: 6342 hits
1456 - Eastern Dispatch 1: 60456 hits
1520 - Eastern Dispatch 2: 5950 hits
1616 - Western Dispatch 1: 49235 hits
1680 - Western Dispatch 2: 4408 hits
1776 - Central Dispatch 1: 53469 hits
1840 - Central Dispatch 2: 4639 hits
1936 - Northeastern Dispatch 1: 114 hits [I believe these are 'on' Northern or Eastern]
2000 - Northeastern Dispatch 2: 6 hits
2096 - Southeastern Dispatch 1: 1738 hits [Dispatched on Eastern or Southern, not certain]
2160 - Southeastern Dispatch 2: 177 hits
2256 - Mid City Dispatch 1: 56021 hits
2320 - Mid City Dispatch 2: 5774 hits
2416 - North City West Dispatch 1: 1480 hits [Probably actually use Northern]
2480 - North City West Dispatch 2: 517 hits