Mexican nationals do not require a visa/passport when entering the United States so long as:
1) They have a DSP-150, B-1/B-2 visa and Border Crossing Card (BCC), which contains a machine readable biometric identifier;
2) They are coming from an adjoining territory (land or sea); and
3) They are applying for B-1/B-2 entry.
For all other situations, a Mexican national must have a passport. 8 CFR §212.1(c); 22 CFR §41.2(g).
I-94 Not Required In Limited Circumstances
Persons admitted with Border Crossing Cards (BCCs) may remain in the United States for up to 30 days without needing an I-94. Under these circumstances travel is generally limited to not more than 25 miles from the border. For Arizona travel is extended to 75 miles. For New Mexico travel is extended to 55 miles. Mexican citizens with no BCCs, but with valid passports and visas, may remain within these border zones for up to 72 hours without an I-94. An i-94 is required for Mexicans in every other circumstance.