I thought they didn't have a popular vote in Colorado in 1876.
I have sent an inquiry to the e-mail contact for the site.
And received the following response (in blue).
Si, le Colorado organisa un scrutin présidentiel en 1876, mais à ravers sa législature (3 élus républicains). Burnham publia les résultats par comtés du scrutin gouvernatorial concomitant "as an approximation to the strength of the two parties in Colorado at that time". C'est lui que j'ai cartographié.
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In 1876, Colorado chose its presidential electors through its legislature (3 republicans elected). However, a gubernatorial election was held that year, and the results by counties of it are given in Burnham "as an approximation to the strength of the two parties in Colorado at that time" (dixit). I mapped the latter.
The statewide result in the gubernatorial race was John Routt (R) 14,154 to 13,316 for the Democrat candidate.
