Figure 4 from: Espinasa L, D. Bartolo N, E. Newkirk C (2014) DNA sequences of troglobitic nicoletiid insects support Sierra de El Abra and the Sierra de Guatemala as a single biogeographical area: Implications for Astyanax. Subterranean Biology 13: 35-44. https://doi.org/10.3897/subtbiol.13.7256

Figure 4 - The Boquillas River has changed its course throughout time. The Boquillas River currently separates the karstic areas of Sierra de Guatemala from the Sierra the El Abra. In the upper part of the figure, the Boquillas River is seen crossing the sierras through the Servilleta canyon. On the bottom part of the figure, a fossil canyon indicates the river's ancient course. Caves that in the past connected the Sierra de El Abra in the south to the Sierra de Guatemala in the north were only recently geologically truncated by the erosion of the new river course. Limestone is restricted to the green forested hills.