Located at 501 Texas Avenue South, this Diamond Shamrock existed from 1989 to around 1998 when it was closed in the process of the Texas Avenue widening. The convenience store probably wasn't even a full brand, not even Diamond Shamrock's "Corner Store" (which existed at least as far back as 1990, but I don't believe for any of the local locations until they were converted to Valero). Afterwards, it was absorbed by the U-Haul dealership (formerly Texas Avenue Moving Center) located at 519 Texas.
Diamond Shamrock had previously been a Sigmor Shamrock store (a predecessor company to Diamond Shamrock, though it might have converted to Diamond Shamrock briefly before being rebuilt, as at least one Sigmor store saw a conversion), as was a few others. The U-Haul dealership appears to have originally been on the site of a Philips 66, and records indicate they used a building leftover to do operations, but after Diamond Shamrock died, they moved to that building and removed the old one for more parking.
The style of Diamond Shamrock (black, multiple colors) had to have been more common but no pictures exist of that style on GasSigns.org.
Prior to Sigmor Shamrock, it was Mais Super Market (sometimes used interchangeably with Louis Mais Grocery), which dates back to the 1930s.
Despite having a Facebook page for this webpage which I (try to) update weekly, I despise Facebook. However, there is one group, "Bryan-College Station: Now and Then", which usually shares my posts with their larger audience, had a bit more on the actual backstory of 501 Texas Avenue South. I can't guarantee that this link will work without the page bugging you to sign in, but the page description has been recreated here with minor edits made for clarity.
We are so happy to share these photos that were contributed by Jeff Mais, who said: "This was the Mais' grocery store that was located at Texas Avenue and University Drive. Actually it was in the path of University Drive and was torn down due to "right of way" for the expansion of the road to the bypass. My grandfather Louis Mais and his wife Lydia started the store in the 30's. It began with Louis running a small gas station. He eventually bought the gas station. Aggies would use the location to catch the bus there and would often asked if they anything to eat. He started selling sandwiches and then just kept adding items that were in demand. Soon he had a small convenience store that made deliveries, and got rid of the gas pumps. Then Louis built a bigger store next door to the old one in the 50's which had a meat market, produce section, and also sold barbecue. My dad Donald tells me that he used to deliver groceries to Bear Bryant when he was the head football coach at A&M. As a child, I remember many people gathering in the back of the warehouse after hours to drink beer and talk about their hunting and fishing tales. The store was closed in 1969 to make way for the new road. Louis and Lydia Mais were hard working people who love the community.
The photos were taken by Donald Mais, who was the son of Louis and Lydia Mais. I am the grandson of Louis Mais (Jeff Mais). I lived in College Station until I was four (1966), then we moved to Houston where I grew up.
As an additional note, the gas station was a Conoco. Despite dramatically shaving the right of way (the building of Mais was almost perfectly where the modern eastbound lanes of University Drive East go, there was enough space at 501 Texas for a new gas station. "Fill-Em Fast" opened in 1972 which became a Sigmor station (#997) which was built in 1978. At some point in the 1980s, Sigmor began to rebrand its stations as Diamond Shamrock. It's unknown if this station ever got the brand changeover, but in 1987 the station was torn down and rebuilt as a Diamond Shamrock (still #997). This is the building that exists today.
UPDATE 08-05-2021: Substantial update on the history of the property. New title and labels.