Foreshocks provide valuable information on the nucleation process and mechanism of impending earthquakes. In this study, we utilized the Match&Locate method to build a high-precision foreshock catalog for the July 2019 Mw 6.4 Ridgecrest, California earthquake. The Mw 6.4 mainshock was preceded by 40 foreshocks within ~2 hours (on July 4, 2017 from 15:35:29 to 17:32:52, UTC). Their spatiotemporal distribution reveals a complex seismogenic structure consisting of multiple fault strands, which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 Mw 6.4 mainshock. To better understand the nucleation mechanism, we conducted a series of analysis for the foreshocks including repeating earthquake identification, rupture directivity inversion, and Coulomb stress change estimation. We identified a pair of small earthquakes with close magnitude, high waveform similarity, and high cross-spectral coherence at the early nucleation stage. However, we cannot confirm if they are repeating earthquakes due to their low magnitude and insufficient sampling rate. Thus, the initial nucleartion mechanism is unclear to us. Following the largest ML 4.0 foreshock, we found the majority of its aftershocks and the Mw 6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. Our study suggests that the nucleation of the Mw 6.4 mainshock can be prominently explained by cascade triggering even though we cannot exclude the possible existence of a minor aseismic slip process at the early stage.