Yep, 10' x 200' per the 1886 Bridges & Buildings book. Construction was similar (though dimensions were not to same) as the docks at Pitkin and Hortense, which we fortunately have pictures of. All three docks were not framed like the current dock outside the Alpine Tunnel shed built after the 1905 fire.
The Hancock dock is not listed in DL&G documents of 1890-1893 that I'm aware of, suggesting it may have been dismantled as early as the timeframe the Hancock depot was moved to Romley during September 1887. Parts of the Hancock dock may have been used to construct a small dock at Romley.
Dave Eggleston
Seattle, WA