April 10, 1869 Joint Resolution of Congress fixes point of union of rails at summit of railroad pass through Promontory Range, but provides for purchase of Union Pacific line, Promontory – Ogden, by Central Pacific. Ogden to be
junction
...
May 10, 1869 Last Spike ceremony. UP decides not to remove from Promontory Summit, which becomes UP-CP junction.
May 11-12, Crews build yards at Promontory; transcontinental railroad opens for service. Promontory City arises. No water found to support trains; water trains come from Corinne and Blue Creek or Kelton on Indian Creek.
June 1869 Chief Engineers Dodge, UP, and Montague, CP, meet and start rebuilding yard to improve operations; CP builds wood frame station that summer
Aug 30, 1869 Western Union completes line north of Salt Lake via Promontory
Sept, 1869 Government commission reports on railroad construction deficiencies, far less than rumored. Meeting of UP and CP officials at Promontory without a decision about moving junction UP builds station/eating house/hotel at Promontory
Nov 17, 1869 Agreement, UP and CP, to relocate junction from Promontory to Ogden
Nov 21, 1869 Vigilantes clean out Promontory City
Dec. 1, 1869 Transfer of Promontory Station and line to Ogden from UP to CP
Dec 6, 1869 First scheduled CP passenger train passes through Promontory to Ogden, and junction with UP trains
So it seems that Promontory was the junction for a few months right after the Golden Spike ceremony, but by December it was as you say, with the CP going all the way to Ogden.
Page 47 has a couple of very interesting photographs taken by Andrew J. Russell in November 1869 showing the railroad eating house (which opened in September), UP ticket and telegraph office and, in the distance, the CP yards.