A 13,000-km2 microplate intervenes to prevent the junction of the Nazca, Cocos, and Pacific plates in the eastern equatorial Pacific Ocean west of the Galapagos Islands. The microplate is rotating clockwise at 6¿/m.y. about an ''absolute'' pole 400 km southeast of its center, so that although its northern margin as a similar motion to adjacent parts of the Cocos plate, its southern margin is 50% slower. The perimeter of the Galapagos microplate is best defined by bathymetry, and has been surveyed with Sea Beam and examined by Deep Tow. Two of the three triple junctions on its margins are ridge-ridge-ridge (RRR) junctions 160 km apart on the crest of the East Pacific Rise (EPR); the most like a classic RRR junction is the Pacific-Nazca-Galapagos intersection at 1¿10'N, where the EPR axis is joined by a narrow volcanic ridge 70 km long and 1 km high. The Cocos-Nazca-Galapagos junction at the west end of the Cocos-Nazca spreading center is inferred to be of the RFF type, but the ''transform fault'' branches are represented by large nontransform offsets. Lack of stable transform faults is related to rapid westward migration of the junction, caused by lengthening of the Cocos-Nazca axis at 60--70 mm/yr. This rate, which was once required to maintain a stable Nazca-Cocos-Pacific RRR junction, has persisted even after birth of the microplate about 1 Ma. Continuing propagation of the Cocos-Nazca axis has opened up the Hess Deep rift basin in the eastern EPR flank in advance of the eruptive propagator tip. This rift valley has a relief of more than 3 km from its uplifted rims to the floor, where severe attenuation exposes basal layes of the EPR crust. The similar Dietz Deep rift basin, at the southeastern margin of the microplate 70 km from Hess Deep, was formed when a lengthening Galapagos-Nazca spreading axis rifted through another part of the EPR flank. ¿ American Geophysical Union 1988