Based solely on the most junior pilot in each base on the seniority list:
Most junior to senior:
SFO-ER7 9/15/2016
ORD-CRJ 9/05/2016
MSP-CRJ 9/05/2016
DTW-CRJ 9/05/2016
FAT-CRJ. 8/08/2016
SEA-ER7 8/04/2016
LAX-ER7 8/04/2016
PDX-ER7 7/07/2016
LAX-CRJ 6/27/2016
TUS-CRJ 6/06/2016
PSP-CRJ 6/06/2016
SFO-CRJ 6/06/2016
SLC-CRJ 5/09/2016
PHX-CRJ 12/08/2015?
ORD-ER7 5/12/2016
DEN-ER7 5/12/2016
COS-CRJ 4/25/2016
DEN-CRJ 4/25/2016
SEA-CRJ 11/23/2015
IAH-CRJ 8/24/2015

This does not reflect how many senior guys are in base. For example, a senior FO in DTW could be higher up percentage wise than if they were in MSP.