Context. In spiral galaxies, star formation tends to trace features of the spiral pattern, including arms, spurs, feathers, and branches. However, in our own Milky Way, it has been challenging to connect individual star-forming regions to their larger Galactic environment owing to our perspective from within the disk. One feature in nearly all modern models of the Milky Way is the Sagittarius Arm, located inward of the Sun with a pitch angle of similar to 12 degrees .Aims. We map the 3D locations and velocities of star-forming regions in a segment of the Sagittarius Arm using young stellar objects (YSOs) from the Spitzer/IRAC Candidate YSO (SPICY) catalog to compare their distribution to models of the arm.Methods. Distances and velocities for these objects are derived from Gaia EDR3 astrometry and molecular line surveys. We infer parallaxes and proper motions for spatially clustered groups of YSOs and estimate their radial velocities from the velocities of spatially associated molecular clouds.Results. We identify 25 star-forming regions in the Galactic longitude range l similar to 4.degrees 0-18.degrees 5 arranged in a narrow, similar to 1 kpc long linear structure with a high pitch angle of =56 degrees and a high aspect ratio of similar to 7:1. This structure includes massive star-forming regions such as M8, M16, M17, and M20. The motions in the structure are remarkably coherent, with velocities in the direction of Galactic rotation of |V-phi|approximate to 240 +/- 3 km s(-1) (slightly higher than average) and slight drifts inward (V-R approximate to -4.3 km s(-1)) and in the negative Z direction (V-Z approximate to -2.9 km s(-1)). The rotational shear experienced by the structure is Delta Omega =4.6 km s(-1) kpc(-1).Conclusions. The observed 56 degrees pitch angle is remarkably high for a segment of the Sagittarius Arm. We discuss possible interpretations of this feature as a substructure within the lower pitch angle Sagittarius Arm, as a spur, or as an isolated structure.