SP used to publish quarterly loco assignment books showing where steam (and later diesel) locomotives were assigned at the end of a quarter. A friend gave me his extras and then allowed me to copy the others. What follows is a yearly total showing the reduction in steam on the SP starting with September 30, 1950.
Western 228
Sacramento 124
Salt Lake 67
Shasta 99
Portland 137
Coast 157
San Joaquin 91
Los Angeles 129
Tucson 81
Rio Grande 68
Total 1181

September 30, 1951
Western 235
Sacramento 80
Salt Lake 70
Shasta 66
Portland 140
Coast 158
San Joaquin 92
Los Angeles 127
Tucson 80
Rio Grande 66
Total 1141

December 30, 1952

Western 228
Sacramento 74
Salt Lake 57
Shasta 64
Portland 125
Coast 126
San Joaquin 97
Los Angeles 138
Tucson 57
Rio Grande 57
Total 1050

September 30, 1953

Western 221
Sacramento 73
Salt Lake 35
Shasta 54
Portland 109
Coast 139
San Joaquin 77
Los Angeles 130
Tucson 43
Rio Grande 28
Total 911 (includes 2 spares on NWP)

September 30, 1954

Western 164
Sacramento 62
Salt Lake 38
Shasta 33
Portland 62
Coast 123
San Joaquin 99
Los Angeles 123
Tucson 3
Rio Grande 5
Total 712

September 30, 1955

Western 154
Sacramento 41
Salt Lake 33
Shasta 7
Portland 29
Coast 119
San Joaquin 86
Los Angeles 1
Yuma 19
Tucson 1
Rio Grande 3
Total 493

September 30, 1956

Western 118
Sacramento 14
Salt Lake
Shasta
Portland
Coast 113
San Joaquin 46
Los Angeles
Yuma 12
Tucson
Rio Grande 3 (3400 class 2-8-0's used on Nacozari)
Total 306



Note the withdrawal of steam from the North, East and South to the Bay Area. Steam was pretty much gone from Dunsmuir after summer of 1955. 2-10-2 3670 was used as a point helper from Dunsmuir to Mt Shasta on the special to McCloud on the 4th of July weekend and shortly after received a 16,000 gallon tender and was sent to Tracy where she worked for another 14 months or so.
I hope this gives a little insight on steams retreat on the SP. As I said before, if anybody would like info on the whereabouts of a particular SP steam loco, email me & I'll try to oblidge.