  For a finite Coxeter group W and a Coxeter element c of W, the c-Cambrian fan
is a coarsening of the fan defined by the reflecting hyperplanes of W. Its
maximal cones are naturally indexed by the c-sortable elements of W. The main
result of this paper is that the known bijection cl_c between c-sortable
elements and c-clusters induces a combinatorial isomorphism of fans. In
particular, the c-Cambrian fan is combinatorially isomorphic to the normal fan
of the generalized associahedron for W. The rays of the c-Cambrian fan are
generated by certain vectors in the W-orbit of the fundamental weights, while
the rays of the c-cluster fan are generated by certain roots. For particular
("bipartite") choices of c, we show that the c-Cambrian fan is linearly
isomorphic to the c-cluster fan. We characterize, in terms of the combinatorics
of clusters, the partial order induced, via the map cl_c, on c-clusters by the
c-Cambrian lattice. We give a simple bijection from c-clusters to c-noncrossing
partitions that respects the refined (Narayana) enumeration. We relate the
Cambrian fan to well known objects in the theory of cluster algebras, providing
a geometric context for g-vectors and quasi-Cartan companions.
