Well OK. If you want the long detailed answer then I guess I can type more than two sentences.
While in Texas you should calibrate your drop chart based upon your muzzle velocity and BC at your local elevation. You have to take into account temperature, humidity, etc in order to determine a correct for Texas drop chart.
You will need to use one of the ballistic computer programs such as Exbal or JBM
JBM - Calculations - Trajectory
Once you have everything calculating satisfactory for Texas and you get to Wyoming you will need to change the inputs according to the weather and elevation at which you hunt if you have a PDA based computer program. Obviously the temperature is going to change during a day and day by day. It may be blowing snow one day Coppertone time the next.
If you do not have a PDA with a ballistics program and you are going to limit your shots to 600 yards then you can built yourself one or more drop charts that will allow you to hit an elk easily. They are pretty big!
What you should do is use Google Earth to find the average elevation at which you think you will be hunting and the minimum and maximum. Then find out what the early morning temperatures are likely to be for those elevations and what the average daily temperature will be.
So for each elevation you should print out a drop chart for the morning temperature and the average daily temperature.
Once you have all of these drop chart printed out you can then find out how much a 10 degree change in temperature makes in bullet strike at 600 yards. You can also figure out how much a 1000 foot change in elevation will make to bullet strike.
At the top of my drop charts I have the temperature and elevation for which it was calculated and then the amount of change that will occur at 1000 yards for a ten degree temperature shift and the amount of change for 1000 ft of elevation change. This way I can move around during the day and still work off of one drop chart. This same technique is good for BDC knobs.