Valleys and the maximum local time for random walk in random environment

Let ξ(n, x) be the local time at x for a recurrent one-dimensional random walk in random environment after n steps, and consider the maximum ξ∗(n) = maxx ξ(n, x). It is known that lim sup n ξ∗(n)/n is a positive constant a.s. We prove that lim infn(log log logn)ξ ∗(n)/n is a positive constant a.s.; this answers a question of P. Révész (1990). The proof is based on an analysis of the valleys in the environment, defined as the potential wells of record depth. In particular, we show that almost surely, at any time n large enough, the random walker has spent almost all of its lifetime in the two deepest valleys of the environment it has encountered. We also prove a uniform exponential tail bound for the ratio of the expected total occupation time of a valley and the expected local time at its bottom.