CONCAN, Texas (AP) — Federal investigators will get their first look Thursday at the scene of a head-on collision between a pickup truck and small church bus in southwest Texas that crumpled the front of the bus and killed 13 senior adults returning from a church retreat.

The Texas Department of Public Safety refused to speculate on the cause of the Wednesday afternoon crash outside Garner State Park, about 75 miles (120 kilometers) west of San Antonio, although one spokesman suggested the truck driver may have crossed the center line.

The fronts of both vehicles were heavily damaged in the collision and the bus was backed up onto a guardrail, with glass and debris scattered around.

Twelve bus occupants, including the driver, died at the scene, DPS Lt. Johnny Hernandez said. Another bus passenger died at a San Antonio hospital. The pickup driver was in stable condition and the lone survivor from the bus remained hospitalized in critical condition late Wednesday, DPS said.

"We are still grieving and we're going to grieve for a while, and we will see what tomorrow looks like and then the next day," Brad McLean, senior pastor of the First Baptist Church of New Braunfels, Texas, told reporters Wednesday. "But we know this: We know the strength of the Lord is going to provide our next steps."

McLean declined to identify any of the victims.

Hernandez said the vehicles collided at 12:23 p.m. on U.S. 83 near the town of Concan after the truck crossed the center line. But at a briefing near the crash site Wednesday night, DPS Sgt. Orlando Moreno declined to speculate on possible causes of the crash, which occurred in a curve of the road where the speed limit is 65 mph.

The National Transportation Safety Board was sending investigators to the scene to determine the cause of the crash, NTSB spokesman Terry Williams said.

DPS Sgt. Conrad Hein said the small bus was a 2004 Turtle Top, though he did not know the specific model. Turtle Top's website features shuttle buses with capacities ranging from 17 to 51 passengers, which they bill as "a great alternative to the standard 15-passenger van." Safety concerns have long surrounded the 15-passenger vans, which are frequently used by churches and other groups, with advocates saying they can be difficult to control in an emergency.

The San Antonio-area church said on its website that the members were returning from a three-day retreat at the Alto Frio Baptist Encampment in Leakey, about 9 miles (15 kilometers) from the crash site.

Church officials were "ministering to family members to help them deal with this tragedy" and counselors will be available Thursday at the church, according to the statement.

Texas Gov. Greg Abbott and his wife, Cecilia, offered their condolences.

"We are saddened by the loss of life and our hearts go out to all those affected," their statement said. "We thank the first responders working on the scene in the wake of this unimaginable tragedy, and ask that all Texans join us in offering their thoughts and prayers."