Research has shown that the lower air pressure due to the altitude in Chaffee County (~ 7000′ elevation in Salida and ~ 8000′ in Buena Vista) will slow performance, due to a drop in your bodies ability to deliver Oxygen to working muscles.
Your times will be about 3.7% slower for a 15 minute race in Salida as compared to sea level (~4.7% for 15 minutes in Buena Vista).
For a 30 minute race, times will be ~4.8% slower in Salida and ~5.8% slower in Buena Vista.
For an hour race, you will be ~ 5.7% slower in Salida and ~6.7% slower in BV.
This assumes a well trained runner that has acclimated to altitude and all other conditions (heat, wind, hills, humidity) being the same. (which they are not…)
What does this mean? One percent of an hour is 36 seconds, which is a big chunk of time in a race!
3.7% of 15 minutes is over 33 seconds.
4.8% of 30 minutes is over one minute 25 seconds.
5.7 % of 60 minutes is 3 minutes 25 seconds.
Your times for races that take you 15, 30 or 60 minutes to finish in Salida will be ~ :33, 1:25 or 3:25 slower than at sea level, respectively and theoretically.