The inherent structures ({it IS}) are the local minima of the potential energy surface or landscape, $U({bf r})$, of an {it N} atom system. Stillinger has given an exact {it IS} formulation of thermodynamics. Here the implications for the equation of state are investigated. It is shown that the van der Waals ({it vdW}) equation, with density-dependent $a$ and $b$ coefficients, holds on the high-temperature plateau of the averaged {it IS} energy. However, an additional ``landscape contribution to the pressure is found at lower $T$. The resulting extended {it vdW} equation, unlike the original, is capable of yielding a water-like density anomaly, flat isotherms in the coexistence region {it vs} {it vdW} loops, and several other desirable features. The plateau energy, the width of the distribution of {it IS}, and the ``top of the landscape temperature are simulated over a broad reduced density range, $2.0 ge rho ge 0.20$, in the Lennard-Jones fluid. Fits to the data yield an explicit equation of state, which is argued to be useful at high density; it nevertheless reproduces the known values of $a$ and $b$ at the critical point.
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