The updrafts generated by air encountering rising terrain can extend thousands of feet above the surface. If you are circling in a valley to gain altitude to clear surrounding terrain, you might as well camp out in a column of rising air. On a windy day, you can generally find one on the downwind side of a valley or the upwind side of a hill. Adding a 500 fpm updraft to your plane's meager 300 fpm rate of climb is like adding a turbocharger, only it's cheaper, lighter and easier to maintain. The point is that you can float a long way if you fail to control your airspeed when landing in rarified mountain air.
Ground effect is an often misunderstood phenomenon.
When thrust exceeds drag, the airplane will accelerate, or climb, or both. That, coupled with an increase in the wing's angle of attack, is the sensation you feel in ground effect. Wingtip vortices result from the circulation of air from the high pressure area under the wing to the low pressure air over the wing. At that portion of the wing, the relative wind is from a more upward direction and lift, which is perpendicular to the relative wind, is tilted rearward. The reward-tilted lift force has a vertical component, which is lifting the plane, and a horizontal component, which is holding the plane back.