Your ammonite probably is...

Desmoceras

Desmoceras had whorls with an almost square cross-section. Desmoceras had very strong and well defined radial ribs that were well-spaced and crossed the entire shell. Weak radial ribs were packed between them. Desmoceras' suture changed as it grew, making identification by suture more difficult. Desmoceras is from the Cretaceous of Texas and California.