C&S Harp evolution:

Many photo dates are approximate, but they don’t indicate the installation date anyway, just the date the stand happened to be photographed.  Where a date range is all that is available, the approximate date shown occupies the middle of the range.

Forks Creek:	~1875:	dark oblong target, notched stand.  DPL X-8469.
Beaver Brook:	~1875:	red & white oblong target, notched stand.  DPL X-19326.
Alpine Tunnel:	~1882:	red & white oblong target, stand indistinct.  DPL WHJ-1425.
Nathrop:		~1882:	red & white oblong target, stand indistinct.  MBII p.286.
Central City:	~18821:	red & white oblong target, notched stand.  DSP&P PS p.64.  
Golden:        ~1882:	single-red-dot target, stand hidden.  DPL X-9783.
Forks Creek:	~18821:	dbl-red-dot target, stand hidden.  DPL Z-3379.  
Chalk Creek:	 1883:	white oblong target, short stand.  DSP&P PS p.9.
Illinois Park:	 1883:	dbl-diamond targets, stands indistinct.  MBII, p.137.
Beaver Brook:	 1885:	dark oblong target, notched stand.  DPL X-7299.
Boreas Pass:	 1885:	target missing, stand indistinct.  C&Sng p.10.
Idaho Springs:  18853:	single-red-dot target, notched stand.  DPL CHS.J3604.
Morrison:		~1885:	dbl-red-dot target, notched stand.  DPL CHS.X4952.
Graymont:		~1886:	dbl-red-dot target, notched stand.  DPL Z-2566.
Idaho Springs:  1887:	dbl-diamond target, eared stand.  DPL CHS.X4553.
Atlantic:		 1888:	dbl-red-dot target, eared stand.  HAT, p.156.
Como:		 1889:	target missing, notched stand.  MBII, p.70.
Robinson:		 1889:	dbl-diamond target, eared stand.  DPL CHS-B288.
Beaver Brook:	~1890:	dbl-diamond target, eared stand.  DPL X-7303.
Breckenridge:	~1890:	white oblong or dbl-diamond target, stand indistinct.  MBII p.158.
Climax:		~1890:	dbl-diamond target, stand buried in snow.  DPL CHS.J922.
Morrison:		~1895:	white oblong target, notched stand.  DPL X-11181.
Fairplay:		~1895:	white oblong target, notched stand.  HLM&TS p.82.
Alpine Tunnel:	 1896:	dbl-diamond target, stand indistinct.  DSP&P PS p.314.
Atlantic:		 1898:	dbl-diamond target, stand indistinct.  DSP&P PS p.117.
Pitkin:		 1900:	dbl-diamond target, eared stand.  HAT p.1662.  
Dickey:		 1903:	target missing, notched stand, 1903.  DSP&P PS p.402.
Garos:		 1910:	dbl-diamond target, eared stand.  DSP&P PS p.299.
Alma:		 1914:	dbl-diamond target, stand indistinct.  HLM&TS p.87.
Como:		 1915:	dbl-diamond target, eared stand.  HLM&TS p.37.
Romley:		~19164:	dbl-diamond target, eared stand.  MBII p.303.  
Kokomo:		 1929:	dbl-diamond target, eared stand.  MBII p.201.
Red Hill:		 1929:	oblong target, notched stand.  MBII p.274.
Kenosha Pass:	 1932:	oblong target, notched stand.  C&Sng p.107.
Pine Grove:	 1937:	oblong target, notched stand.  C&Sng p.142.

Notes:
1. Presence of Congdon stacks indicates 1880 - 1885.
2. Derail in same picture has white oblong target and a notched stand.
3. Date ascertained via track alignments on Sanborn insurance maps.
4. 3rd mill location indicates post-1908; tracks abandoned in 1924.

References:
C&Sng: C&Sng, Mallory Hope Ferrell.
DPL: Denver Public Library digital collections.
DSP&P: Denver, South Park & Pacific, M. C. Poor, E. J. Haley.
DSP&P PS: Pictorial Supplement to Denver, South Park & Pacific, R. H. Kindig, E. J. Haley, M. C. Poor
HAT: Historic Alpine Tunnel, Dow Helmers
HLM&TS: C&S High Line Memories and Then Some, Tom and Denise Klinger.
MBII: The Mineral Belt, Volume II, David S. Digerness.