On closer look the two could be the same. The text describes Camp Cooper as being 170 mi, north of Ft. Mason. It also says it was on the clear fork of the Brazos River, 35 miles from the point of its junction with the main stream. According to the Texas fort map I found that would make Camp Cooper almost due east of Ft. Mason. Comparing the modern day map of Texas that could be about mid-way between Austin and Waco.
http://www.lib.utexas.edu/maps/historical/tex_fedforts_1848.jpg
Note that the fort map doesn’t show any forts in the area described above. Maybe Lt. Hood and Lt. Col. Lee scouted a site for a fort that wouldn’t be built until the 20th century.
I can spend days researching this kind of stuff.... consumes a lot of my time, road trip !!
Thanks !
Upon further review I believe I was right the first time. Cooper is marked on the fort map I linked above north of Ft. Mason and there is a fork in the Brazos up there. I was looking at the wrong fork near the present day Ft. Hood.