From trips above 14K on the ground (Pikes Peak) and near that altitude in the airplane, as well as exertion at altitudes around 10-12K (skiing), my first indicator is tingly lips, gums, teeth and a numb face.
Last summer, crossing Hagerman Pass from KASE to KLXV I started to feel this way slightly during the (way less) than 30 minutes it takes above 12,500' to make the crossing. With a CFI on board who was also feeling the effects, I didn't dilly dally around up high after getting over to the other side. And I live at 6050' MSL.
I should have brought the O2, and that's what I learned amongst a whole bunch of other things that day. Better to have it along and be using it, than wish it were along and feeling a little "weird". Or having a headache later. Or any of the other symptoms of altitude sickness. I didn't have any that day, but I have before up in the rocks to the West, in the car.
Pattern altitude for fixed-wing aircraft is 10500 MSL at KLXV. You have to lose about 3000' of altitude in about 5 miles. It's a fun ending to the long slog up the KASE side.
And whoever thought publishing THIS was a good idea, has way bigger brass ones than I'll ever have:
http://204.108.4.16/d-tpp/1106/09146G16.PDF
When the missed approach procedure starts with "Climb to 16000..." - wow. Just wow.
Anyone know anyone who has this approach in their logbook in actual? Insane.
Hagerman Pass (the marker is on the road... look slightly north of that for the power lines that cross over the top East-West, and KLXV is on the right to the East in this map) is here:
http://maps.google.com/maps?q=Hager...client=safari&geocode=FdwiVwIdMi-n-Q&t=h&z=12
You follow the power lines over the top of the pass, and end up over Turquoise Lake during the descent. Wind is almost always West to East, so significant turbulence and rotors can be found on the KLXV side in any winds at all.
Zoomed out a bit, KASE is visible on the left. The route is "down valley" to the northwest out of KASE until you have enough altitude to cross the ridgeline to the north, near Basalt, then backtrack along that ridge, now on the north side, shuttle climbing if necessary until you reach Hagerman Pass at just under 13,500 MSL.
http://maps.google.com/maps?q=Hager...client=safari&geocode=FdwiVwIdMi-n-Q&t=h&z=11
It's a hoot of a trip with a good mountain CFI. Corona Pass, 20V, KGWS, KASE, KLXV, Badger Mountain RCO.
It put a smile this big ...
... on my face.