Hydro relies on a pressure difference. This means you want the turbine located at the lower reservoir, which is going to be tricky with an oil well. Oil fields are not a hole filled with oil but instead are just porous rock, which greatly limits the flow rate you can achieve from a single well. Oil fields are already pressurized, so you'd actually need to put in energy to get water in there.
And of course you'd be contaminating the water with oil and gas, which makes the upper reservoir a bit of an issue.
Ironically Colorado is a very hard partner to trade with. The major consumer (Denver) is in the center of the state. The entire eastern half is an empty plain and the western half of Kansas is a slightly less empty plain. From population center Kansas City to Denver is about 600miles, make energy trade a little impractical. They make a ton of their own wind energy on their open plain, and they were late adopters; they learned a lot from Kansas's expensive mistakes on wind power.
If land is not overly expensive, then vertical bifacial solar can be quite viable. With snow or a light non-vegetated surface you should expect around 15% capacity factor in the worst month at 40 degrees and it will be skewed heavily towards morning/evening and slightly toward cloudy days compared to monofacial.
Doesn't get rid of the fossil fuels on its own, but should be cheap enough to displace most coal that remains after wind at a significant profit.
Here in Kansas we have a ton of wind energy production and we’re lucky enough to have a nuclear reactor as well. It’d really be nice to store that, but we have no mountains. We have a rolling plain in the middle of the state but even the highest/lowest delta is like 200-300 ft (I made that number up).