Systems-level organization in spontaneous infra-slow (<0.1Hz) brain activity, measured using blood oxygen signals in fMRI and optical imaging, has become a major theme in the study of neural function in both humans and animal models. Yet the neurophysiological basis of infra-slow activity (ISA) remains unresolved. In particular, is ISA a distinct physiological process, or is it a low-frequency analog of faster neural activity? Here, using whole-cortex calcium/hemoglobin imaging in mice, we show that ISA in each of these modalities travels through the cortex along stereotypical spatiotemporal trajectories that are state dependent (wake versus anesthesia) and distinct from trajectories in delta (1–4 Hz) activity. Moreover, mouse laminar electrophysiology reveals that ISA travels through specific cortical layers and is organized into unique cross-laminar temporal dynamics that are different from higher frequency local field potential activity. These findings suggest that ISA is a distinct neurophysiological process that is reflected in fMRI blood oxygen signals. Display omitted •Wide-field Ca/hemoglobin imaging reveals infra-slow spatiotemporal trajectories•Infra-slow activity (ISA) has distinct dynamics compared to higher frequencies•The direction of ISA trajectories depends on state of consciousness•Laminar electrophysiology shows that ISA travels through distinct cortical layers Mitra et al. measure spontaneous infra-slow activity (ISA; <0.1 Hz) in mouse cortex using wide-field optical calcium/hemoglobin imaging and laminar electrophysiology. They find wide-scale cortical spatiotemporal trajectories in ISA that are state-dependent and distinct from higher frequency neural activity.