Turns out Covenant United Methodist Church is the owner of the dirt parkway that houses the "Welcome to Pomona" sign. I spoke with Pastor Jae Lew tonight. Pastor Jae was immediately receptive to the idea of members of his church working alongside community volunteers to landscape the area.
Pastor Jae said that his church has been looking for ways to reach out to the community. He mentioned, for instance, their recently setting up scholarships for youth living in Pomona.
Pastor Jae and I exchanged emails so that we can start planning the logistics, both admitting that we would need input from more experienced gardeners. He does not think there are sprinklers there btw. Pastor Jae said his church council meets on Saturday, so he will tell them about the idea at that time.