My concern is this.... while the charts may say that sunset is at ...say... 1800 on a specific day.... is that the time that the sun is going to physically set or is that the time that we're going to lose light?

For instance... I know, in my local mountains, that sunset is generally around 5:30ish this time of year... but there are certain areas because of the ridgeline that you lose truly usable daylight at about 4:15 or 4:30.... and if you're going to be out after 4:30 or so you darned well better have a headlamp with you...

That's the kind of information that I'm looking for concerning the area I'm taking the boys to this summer...