Extensive research into high temperature superconducting cuprates is now focused upon identifying the relationship between the classic 'pseudogap' phenomenon^{1,2} and the more recently investigated density wave state^{3-13}. This state always exhibits wave vector Q parallel to the planar Cu-O-Cu bonds^{4-13} along with a predominantly d-symmetry form factor^{14-17} (dFF-DW). Finding its microscopic mechanism has now become a key objective^{18-30} of this field. To accomplish this, one must identify the momentum-space (k-space) states contributing to the dFF-DW spectral weight, determine their particle-hole phase relationship about the Fermi energy, establish whether they exhibit a characteristic energy gap, and understand the evolution of all these phenomena throughout the phase diagram. Here we use energy-resolved sublattice visualization^{14} of electronic structure and show that the characteristic energy of the dFF-DW modulations is actually the 'pseudogap' energy \Delta_{1}. Moreover, we demonstrate that the dFF-DW modulations at E=-\Delta_{1} (filled states) occur with relative phase \pi compared to those at E=\Delta_{1} (empty states). Finally, we show that the dFF-DW Q corresponds directly to scattering between the 'hot frontier' regions of k-space beyond which Bogoliubov quasiparticles cease to exist^{31,32,33}. These data demonstrate that the dFF-DW state is consistent with particle-hole interactions focused at the pseudogap energy scale and between the four pairs of 'hot frontier' regions in k-space where the pseudogap opens.