  According to a conjecture, all 5d SCFTs should be obtainable by
rank-preserving RG flows of 6d SCFTs compactified on a circle possibly twisted
by a background for the discrete global symmetries around the circle. For a 6d
SCFT admitting an F-theory construction, its untwisted compactification admits
a dual M-theory description in terms of a "parent" Calabi-Yau threefold which
captures the Coulomb branch of the compactified 6d SCFT. The RG flows to 5d
SCFTs can then be identified with a sequence of flop transitions and blowdowns
of the parent Calabi-Yau leading to "descendant" Calabi-Yau threefolds which
describe the Coulomb branches of the resulting 5d SCFTs. An explicit
description of parent Calabi-Yaus is known for untwisted compactifications of
rank one 6d SCFTs. In this paper, we provide a description of parent
Calabi-Yaus for untwisted compactifications of arbitrary rank 6d SCFTs. Since
6d SCFTs of arbitrary rank can be viewed as being constructed out of rank one
SCFTs, we accomplish the extension to arbitrary rank by identifying a
prescription for gluing together Calabi-Yaus associated to rank one 6d SCFTs.
